Concrete framed problems and solutions

Reinforced concrete framed construction problems and solutions

Concrete framed buildings can be up to 60 years old in Galicia, but even some built very recently suffer from the common problems of this build type, which are:

  • Humidity and damp problems throughout, especially if built into sloping ground with a ground supported floor, and with the lack of a ground floor damp proof membrane a particular problem. The prevalence of leaks and rising damp comes down mostly to original build quality.
  • Cavity walls that do not have weep holes and therefore retain their moisture, and steel reinforced concrete lintels within these cavity walls that are corroding for this reason.
  • Poor to no insulation all round leading to extremely poor thermal performance, with ground supported floors a particular problem.
  • Utilisation of a  cavity wall system but as both leaves are built within the concrete frame structure there is a huge amount of thermal bridging.
  • Widespread mould infestations due to condensation and ventilation problems.
  • Inadequate and/or antiquated heating systems.
  • Inadequate and/or antiquated and unsafe electrical (eg. insufficient sockets, no earth) and plumbing (may well contain sections of lead piping buried within walls) installations. All of this will be buried with walls.
  • Lack of internal insulation and all interior surfaces being flat and hard (ie. tiled floors, concrete rendered walls and ceilings) gives unpleasant acoustic environment and little barrier to the passage of low frequency sound throughout the building.
  • Internal woodwork (not normally structural but roof can be timber beam supported in old houses) often has some woodworm infestation.

In general concrete framed buildings can be renovated quite cheaply to make reasonable if not very thermally efficient houses, and with a bigger spend can be turned into good quality modern homes.
Occasionally you will come across a concrete framed building that has serious structural issues, such as this one in our property search service case study, but the vast majority of Galician frame builds are somewhat overengineered and are structurally sound.

You might imagine that recently constructed houses are better built and utilise more modern technology than older ones but in fact this often isn’t true, although anything built by a good quality construction company in the last 10 years is probably a step up. More than anything, the determining factor is original build quality.

The major benefits of concrete framed houses are:

  • Non-supporting external and internal walls make it very easy to cut holes for new windows and doors, merge rooms or otherwise remodel the house layout.
  • Coastal houses from the 1970s, 1980s and early 1990s tend to have the very best situations as coastal plots were cheap to buy at this time and there were few planning restrictions – even if you can find an equivalent plot today you may well not be able to build on it.
  • In general these houses are big (250m2 is normal) and sit in large plots (2000-4000m2 is typical even near the coast, although recent builds will have much smaller plots) with a good degree of privacy.
  • Existing buildings have existing permissions, although you should always check that any house you are interested in is in fact legally built, and you can often renovate them using just minor building works permissions (ie. no expensive architect’s proyecto needed).

Solutions for renovating a typical Galician frame build house into a modern, healthy, comfortable and also reasonably energy efficient home are given below within a typical (in order) restoration schedule.


Never start building work without a fairly detailed (ideally completely detailed) plan of your final building.

If you’re applying in advance for all your building permissions, as the law dictates, then you have no choice but to do this, but even for smaller, internal renovations that may fly under the official radar there should always be a clear and thorough plan.
This provides focus, gives a visual context for communication with builders, allows things to be checked as you progress, and allows electric and plumbing conduit and circuitry for the final system to be placed as you go.

It also allows you to ensure that materials are ordered and on site for when they will be needed so you don’t have workers hanging around with little to do or even disappearing to another job from which you struggle to retrieve them.

In short, a good plan will save you time, money and hassle and will produce a better final result.

Fix the roof

Almost all concrete framed houses will have a roof made as follows:

  • The roof structure is actually a cast (aerated, but still heavy and with poor thermal performance) concrete slab.
  • On top of this will be cement fibreboards bolted onto the slab. If a house has a (more expensive) slate roof these will be fixed to batons mounted on the slab, or occasionally bolted directly onto the slab.
  • Sometimes cement fibreboards will be left exposed or painted with waterproof sealant, but normally cement or clay tiles will be laid on top (stuck down with expanding foam and with wire retaining clips).
  • Good quality roofs will use appropriate ridge and edging tiles. Poor quality roofs will use a line of regular concrete tiles concreted onto the ridge and cast concrete for the edges.
  • In all but the newest builds velux windows are rare, which misses out on potential light, views and ventilation benefits if there are rooms directly below the roof. Dormer windows are more common but tend to be quite small.

Making a roof this way is a fast and quite cheap way to weatherproof the shell of the building, and it also impresses many Galicians because they assume that that much concrete must be very strong and therefore good!

From a modern building technology and environmental point of view this is an appalling way to construct a roof – far more material than structurally necessary is used at large environmental cost, and whilst having three full layers of roofing (normally) keeps the weather out well enough the thermal performance of these roof is dreadful, leaking heat in the winter and absorbing sun all day and then radiating into upper floor rooms (normally the bedrooms) all night in the summer when it’s often too hot to start with.

Unfortunately improving this type of roof is normally a lot of expense for a fairly small gain and therefore if you have a roof of this kind that’s in good condition renovating it is normally very low on the priority list.

If, because the roof needs major repair or just because you want to and have the budget for it, you do want to improve this type of roof, it can be done as follows. Note that there are many types of excellent roof sheeting systems available, but here I’ve described “uralita y tejas” because it’s cheap, readily available and the local workforce knows how to use it.

  • Take the opportunity to get rid of any asbestos – cement fibreboards manufactured before the year 2001 probably contain asbestos. Whilst this asbestos isn’t actually dangerous if covered and therefore not allowed to degrade, it is much more brittle and prone to cracking than modern cement fibreboard and the liklihood is that in the future there will much stricter controls regarding it’s disposal or re-use (at the current time your builder will probably just take it away for you for free and it will get re-used on a shed somewhere).
    Therefore you will need to strip off the tiles and the fibreboard to leave just the concrete roof plate. Whilst this is exposed you should also inspect it for any problems and fix anything you find.
  • Consider adding velux windows – velux (alternative make Fakro is slightly cheaper and they seem to leak less often) windows add light, ventilation and views to rooms below a roof, and adding these at the same time as replacing a roof makes sense.
    Unfortunately there are two major problems with doing this. Firstly you have to be sure that you can cut away a part of your roof slab without compromising it structurally (this depends on how it is constructed), and second whilst a roof can be replaced with minor building works permission the addition of any windows changes it to major building works permission, which requires a proyecto from an architectural technician.
    If you add velux windows, ensure they are fitted based on the increased (because of the inclusion of insulation) height of the reconstructed roof.
  • Add insulation and a breathable membrane under the fibreboard – the only sensible place you can add insulation to a concrete slab roof is between the slab and the cement fibreboard.
    To start constructing your renovated roof lay a one way breathable membrane directly over the roof slab, sealing overlapping sections with double sided tape.
    Next, lay a layer of rigid insulation (normally extruded polystyrene tongue and groove slabs) on top. The thicker this insulation the better, but what normally limits it (to normally 5cm) is the length of screws available to fix the fibreboard to the slab and also the available thickness of insulation slabs.
    On top of the insulation use screws complete with the washer caps designed for securing fibreboard to fix the fibreboard through the insulation to the slab. Squirting some silicon sealant down each screwhole can help protect the integrity of the breathable membrane.
    One additional point to note, ensure that the fibreboard corners are cut as per the manufacturer’s instructions to avoid board pileup where four overlap.
  • Use ridge, edge and eaves fibreboard pieces – cement fibreboard is actually part of a very good, complete roofing system. In Galicia, however, very few people use the ridge, edge and eaves pieces, preferring just to cover these vulnerable edges with a layer of concrete with tiles on top. This more or less works, but the fitted pieces are better.
  • Consider utilising the ventilation potential of cement fibreboard – I’ve never seen this done anywhere else so perhaps it’s my invention? As a roof is constructed at a pitched angle the form of cement fibreboard means that a natural chimney effect will occur if the top and bottom of the fibreboard is left open for the passage of air. As the fibreboard’s area of contact with the building is quite small, and as this contact is with rigid insulation, this chimney effect is capable of removing most heat from solar gain from the roof structure. It also has the advantage of removing any moisture (condensation or humidity tracking out from inside the building) from the underside of the fibreboard.
    I have no idea why this system isn’t widely used, as from having it on my house I can testify that it works very effectively. The only issue you have to watch for is to guard all intakes and vents sufficiently to stop birds and mice from getting into them.
  • Add tiles? – From a functional and environmental perspective painted fibreboard (it can be bought pre-painted) is sufficient to form a good roof with a 50 year lifespan. To conform with planning permission requirements, however, you are normally required to add tiles on top …although many people in rural areas ignore this requirement without any negative consequences.
    Concrete tiles are readily available to fit on top of fibreboard in a number of garish colours or, worse, fake antique effects. You may also be able to find ones made out of actual clay for a more authentic patina and colour.
  • Guttering – To finish a Galician roof a good guttering/drainage system is essential and should also be kept clean and clear. Plastic or aluminium drainpipe sections are available in builders merchants but the best system (avoids junctions which are weak spots) is a single piece aluminium drainpipe that is formed on site.

Expose and fix the outer walls

Many concrete framed houses in Galicia are built into hillsides. It is pretty much guaranteed that the inside of any wall that has earth against its outside will have a damp (and mould) problem.

It is generally always an improvement to remove any earth piled against an outside wall, but in some cases it may not be possible (eg. too close to a road) or it may not be desirable if there are external constructions (stairs, outhouses, entrance paths, etc.) built on top of the ground you would have to remove. This job is normally done with a hired earth mover and driver, and spend some time watching the driver and don’t let him too near the house with his digger if you have any doubts about how accurate he is with it.

Once you have as much of the outer walls exposed as you can/want, fix any cracks, gaps, badly done repairs, etc., scrape off any old and flaking paint and, ideally, leave exposed over the summer to allow your walls to dry out thoroughly.

Although it is hard to do effectively without knowing what is inside the cavity, if your house doesn’t appear to have weep holes to let any moisture collecting on the floor plate inside the cavity out, consider (it depends on surface cladding/coating, moisture levels at the base of the internal walls and on how the two skins of the wall are constructed) making some by drilling small holes diagonally upwards to pierce the cavity floor.

This is also a good time to cut holes in the outer walls for any additional windows or doors, extractor fans, ventilation systems or chimneys, although this can easily be done later for security or weathertightness.

Cavity wall insulation

Although it can lead to damp ingress and although it doesn’t fix the huge thermal bridging problems most Galician concrete framed houses have, normally the benefits (healthier, more comfortable, more thermally efficient building) of putting in cavity wall insulation significantly outweigh the costs. Before you get this ensure that you have no open holes to your wall cavity.
This insulation is lots of little polystyrene balls sprayed in through holes drilled into the outer walls. Modern cavity wall insulation should always have a coating on it that will make it stick together when it sets – if it doesn’t then any hole you make in your internal wall will see an split bean bag type avalanche occur.
When drilling into your walls, try to measure the depth of your cavity. Multiply this by the area (minus windows, doors and structural columns) of cavity walls to get a total cavity volume, and check to see that the amount of insulation sprayed in roughly matches this. If it doesn’t your cavities may well be snarled up with mortar snots and the insulation material getting jammed in them. Unfortunately the only easy way of discovering this also tends to mean that the problem has just become even harder to fix! The only way of doing this is to open a hole in the inside wall big enough to allow you to clean out the mortar snots from the cavity …and obviously the polystyrene will either come out too or will have set with lots of gaps making it impossible to pour in more.
For this reason, any time you are making or can access large holes in the wall (eg. for a window), take the opportunity to clean mortar snots out of the cavity and also completely clear the base of the cavity (and make good weep holes) as much as possible.

Waterproof the outer walls

To waterproof outer walls effectively a functioning damp proof course is needed to prevent rising damp. Most Galician houses other than those built comparatively recently (2000s) don’t have one of these and so it is necessary to retrofit one by injecting a specialist silicon at roughly 10cm intervals around the whole wall base at 15cm above ground level.

The external walls, now hopefully nice and dry, should be sealed either by painting a waterproof sealant on top (either an all in one or with paint on top of that) or by cladding the walls with a non- water permeable material such as stone or tiles. If you either have or have retrofitted a damp proof course then don’t waterproof below it (normally the last 15cm down to ground level) as this section of the wall will be subject to rising damp and needs to be able to breathe.


(Ground supported) ground floor (with plumbing and electric ductwork)

If you have a traditional, unrestored ground floor (ie. a concrete plate with tiles on top and no damp proof membrane or insulation), and especially if you want to move the existing ground floor walls around, it is worth considering redoing the ground floor.

As the floor slab on a frame build house will normally be a structural element (acting as a ring beam for the supporting pillars) you can’t remove it and you therefore can’t take the floor level down to give you height for a new floor. What you can do is keep the existing ground floor as a nice level base to make a new one on top of.

If you don’t redo the ground floor (or a similar solution as below) then you will have a perpetually cold and damp ground floor and this will greatly reduce your building comfort and health.

To make a new ground floor the first thing you need to do is work out your heights. When building on top of an existing ground floor the key factor in determining this is normally your staircase. If (as is normal) it’s a cast concrete staircase and you don’t plan on changing it then the easiest thing to door with the floor is to go up a total of one step in height. As a typical step is around 17cm high this works out well for 8cm insulation + 8cm slab + 1cm flooring.
The downside of raising the ground floor is that all your windows and doors will now be at the wrong level. Doors can be retained and a lowered section of floor kept around them with one step up to the new height, but windows will often need altering. This factor is often prohibitive and means that the sensible alternative is to fit a damp proof membrane over the top of the existing floor (bonded into the walls) and click flooring on top, for which you only need a total height loss of 1cm. You don’t of course, do this at this stage as it would be entirely destroyed by subsequent building works.

If laying a new floor slab, the first layer you put down is rigid insulation. Complete continuity of insulation is important so laying two layers of 3,4 or 5cm (more is always better) tongue and groove insulation at 90 degrees to each other works well. You also need to fit insulation all around the sides to the height you will pour your new concrete slab to (normally 10cm if using regular concrete, but as low as 6cm is possible with specialist products). If you are careful fitting the insulation round the sides you can also use these sides as reference heights for levelling the slab when you pour it.

On top of the rigid insulation the next layer is the damp proof membrane, which sounds hi-tech but is actually nothing more than thick black builder’s plastic. If fitted carefully this layer also functions as an adequate radon barrier.

Builder’s plastic comes in widths up to 8 metres and so in most cases you should be able to do the whole ground floor in a single piece. You need to leave at least enough extra at the sides to cover the insulation edges and bond into the stone wall, but for additional protection against damp you can leave around 1 metre extra at each side (how this is used is described below).

Over the plastic goes steel reinforcement with feet to set it in the centre of the slab. If you are using conventional concrete then you will need to leave expansion joints in your slab. These can be created by setting thin (eg. 1cm) vertical strips of wood fibreboard in the slab and then either levering or angle grinding these out after the slab has set. If done carefully these can also be used as height references for levelling.

If you know the location of any new stairs or support columns (not that these should be necessary) then add appropriate steel reinforcement that will protrude above the slab to be used as footings for these things.

If you have ground floor bathroom or kitchen plumbing (eg. drainage) that is best laid below floor level then this should be laid at this stage. Likewise, if you want to pass any electrics below floor level then lay the ducting for them at this point.

Be aware when you place plumbing and especially fragile electric ducting that builders will be tramping around unable to see where their feet are going when shifting and levelling the concrete for the slab, so place ducting and plumbing where it won’t get damaged (eg. cut it into the rigid insulation below the concrete slab) or protect it with suitable boards for the builders to walk on.

The next step to make your new floor is to pour the concrete, but if you are laying a new ground floor slab I would always recommend fitting underfloor heating tubing (eg. 16mm qualpex) into it.

The expensive way to do this is to buy insulation (put this layer above the damp proof membrane) that has the forming for pipework moulded into it. The cheaper and actually better way is to set the steel reinforcement at a slightly lower height (eg. 3cm in a 10cm slab) and zip tie the tubing to it.

The tubing should be laid without joints in the slab, in circuits for each planned room, none of which should exceed 100 metres in length, with sleeving where it crosses an expansion joint and at 10-20cm centres (depending on the heat of the water you intend to circulate in your system; hotter water = bigger spacings). 20cm, handily, is the grid width of standard steel reinforcement.

Plan carefully where you want your tubing to exit the slab, and label the pipes carefully!

Before you pour the concrete it is advisable to pressure test the underfloor heating tubing for leaks. Once that is done order a sand (not coarse aggregate) and cement (plus waterproofing additive and plastificant is recommended) load of concrete of perhaps 5% more than your calculated volume for the floor slab, and look forward to a merry few hours of concrete shifting and levelling.

It’s also a good idea to prepare a place elsewhere to use any leftover concrete (eg. an outbuilding floor or similar).

If you can locate a concrete supplier whose lorry has a good hose to get it directly where you want it then things will go more easily and quickly – this is worth paying extra for.

Once your concrete is poured and levelled leave it for several days (the longer the better, a few weeks if you can) applying a light spray of water on each of the first few days after pouring and ventilate the building as much as possible. Then, seal the floor with a concrete sealant.


Finally, bond in and trim off your surplus damp proof membrane. The higher you can take this up the inside of the external walls the better, as it guards against both rising damp and any radon. If you plan to fit skirting boards of eg. 10cm height then use that full 10cm to take the membrane up the walls.

Even better, if the idea of half height (or higher) panelling or plasterboard finish, perhaps with rigid insulation behind, on the inside of the walls appeals, take the membrane as high up the walls as you can before bonding it in.

To bond the membrane into the wall, score or angle grind out a crack (not so deep that it goes right through the brickwork – note that inner leaf brickwork may be as thin as 3cm) for it, insert it into this and then mortar the crack in.


Construction and finishing of internal walls and plumbing/electric ducting

As all your floors should now be complete except for the final surface you can now move on to any repairs or alterations to your internal walls.

Destroy, build and modify the internal walls as necessary and then fit any plumbing sections and electric conduit that need to be wall embedded into them (assuming they are the standard hollow brick, normally of 6cm width but sometimes just 3cm) and the inner leaf of the exterior wall before rendering and sanding them smooth.
The type of bricks commonly used for non- load bearing walls in Galicia are mostly hollow with cavities sized for fitting electrics and plumbing into, so this isn’t a difficult operation, just really dusty.
Although plastic pipes shouldn’t degrade when mortared in, using a non-reactive sleeve never hurts, and if you use copper pipes you should always do this.

Nearly all the plumbing is installed at this point with the appropriate mounting points (with stop taps) for all plumbed appliances, sinks, etc.. Whilst many plumbed appliances are standardised or connected to plumbing points with flexi-hoses, it is still a good idea to have already bought the appliances to be used so you can check that the plumbing points are where they need to be for the actual appliance you will be fitting there.

It goes without saying that you should pressure test all plumbing systems before rendering over the top of them.

Delay sealing the wall surfaces to allow the walls to dry thoroughly – sealing the wall surface helps prevent the wall from absorbing moisture but it also prevents a damp wall from drying.


Dry out the building (possibly fit windows and doors)

Unrestored Galician buildings generally have too high a moisture content for health and comfort at the best of times, and as using concrete and plaster puts more moisture into the structure the next step is to dry the building out.

Good ventilation in warm, dry summer weather works well, but to really get the moisture content down sealing up the building and running dehumidifiers is the optimum solution.

If whatever existing windows and doors there are aren’t substantially airtight (with taping if necessary) then this is a good time to fit new doors and windows. If the existing ones are airtight and also adequate for building security (tools and building materials in a non-occupied building are a tempting target) then you would generally want to leave fitting new doors and windows until later on so that they don’t get dirtied and damaged by subsequent works.

Using a hygrometer to measure, aim to get relative humidity down to 40% or less for a couple of weeks to let the structure dry thoroughly.




Spanish regulations make a number of requirements for electrical installations, some of the most relevant to home installations being:


Lighting circuits must use 20mm conduit, 1.5mm2 wire, and have phase (brown, normally white for switched), neutral (blue) and earth (green/yellow) connections. A max 10 amp fuse is used with this specification.

Socket (10 amp) circuits must use 25mm conduit, 2.5mm2 wire, and have phase, neutral and earth connections. A max 16 amp fuse is used with this specification.

Ovens and other high power appliances have specific requirements according to their ratings.

All switches and sockets must be connected on a spur to the circuit via a junction box at the top (<50cm from ceiling) or foot (<50cm from floor) of the wall. The main circuit should run straight from junction box to junction box.

Bathrooms have exclusion zones around wet areas where electrics cannot be present.

You can find the full set of Spanish electrical regulations on the government’s website or, in a far more readable form, the principle ones for home installations in this very useful webpage from DIY store Leroy-Merlin.


In a concrete framed building divided internally with brick walls the electrical conduit, junction boxes and switch and socket backs are normally all embedded into the walls. You can fit a surface mounted system if you prefer, but as embedding the system is cheaper (surface mounted components cost more), safer and looks better it’s not a conventional choice. If you do prefer a surface mounted system then leave the electrical installation until after the painting and decorating has been done.

As it’s far easier to pull electrical wiring through conduit before it gets fitted, you can also install all the point to point wiring at this point rather than laboriously tugging it all through later on. This applies especially if you prefer to use solid core wiring (which is slightly cheaper and arguably better).

Electricians are expensive and using them to fit conduit is an unnecessarily expensive way of building. Instead, agree a complete electrical plan and materials specification with a registered electrician and then have the conduit (plus wires if you want) and junction boxes fitted by someone less expensive (eg. whoever is doing your internal walls plasterwork) before getting the electrician back in nearer the end of the project to connect up the fuse box and the fittings and give you your electrical safety certificate. Most electricians are happy to work this way, but of course always check first.



Once your building is sufficiently dry, seal the plastered internal wall surfaces with a plasterwork sealant. You should also seal any concrete floors that will have floating floors on top (but not ones which will be tiled).

Ensuring that you seal surfaces properly serves a number of useful purposes:
* Sealed surfaces help prevent the absorption of airborne moisture by the walls.
* It takes much less paint to cover a sealed surface
* Sealed surfaces are harder for mould spores to lodge and procreate in
* Sealed wall surfaces are harder and more resistant to damage from knocks and scrapes
* Concrete floors with a floating floor on top will continually leak cement dust if not sealed



Tiling can be left until after painting, but as tile cement can be messy and as tiles are by the nature easy to clean, tiling is normally done at this point.


Generally, but especially if fitting a tiled floor over an underfloor heating system, remember to leave an appropriate expansion gap around the perimeter of the floor.


Painting and decorating


Paintwork and decorative finishes should always be applied only to dry, sealed surfaces.


In Galicia it is generally sensible to use anti-mould paint. If you don’t, and especially if you use a matte paint with a textured surface, then you will need to be extremely careful to maintain a low humidity environment within the house in order to stop mould gaining a foothold on the wall.


Floor finishes and carpentry


Carpentry should be measured to exactly fit finished locations, and all possible sanding and varnishing should be done off-site.


As timber is easily stained by paint and wood very vulnerable to damage from builders and heavy materials, carpentry is normally left until this late stage.


Floating floors should also go in as late as possible for the same reasons, and these should have an expansion gap around the edges covered over by skirting boards.


Electrical and plumbing fittings and fitted furniture


The final work on your project is to fit the electrical fittings, bathroom fittings and kitchen furniture.