New build housing is subject to part L building regulations. This makes life easy as house builders know what level of insulation is expected and building control are there to make sure they comply.
Extensions and conversions are also subject to modified building regulations but building control cannot ask that thermal insulation in the pre-existing part of a house be improved. This can lead to one part of a house (sometimes even one part of a room) being well insulated while other parts are not. Yet, having invested money to insulate the new part you’d be well advised to try and improve the energy efficiency of the remainder.
On listed buildings and in conservation areas, Conservation Officers can overrule building control by, for example, insisting that historic glass is left in windows rather than be replaced with double glazed panels.
Lastly, building control do want to see improved U-value for restored and renovated properties even if they have been previously habited. Of course if none of your restoration work is structural you don’t really need to involve building control. Even if you do, no U-value specification for restoration is vague and improvement is limited to what is deemed “technically, functionally” and economically “feasible”. In our experience this feasibility is left largely to the criteria of the builder with building control accept anything were an improved U-value has been achieved.
This leaves it to redeveloper or home owner to decide on how much effort to put into insulating. For homeowners there is the incentive that investment will reduce heating bills. For redevelopers there is, in theory, the inducement that a better EPC will improve the saleability of a property. In practice, there is consensus amongst estate agents that no one pays much notice to EPCs when buying restored property.
So it is down to the redeveloper to decide how much of his/her money he wants to put into insulating someone else’s home and saving the planet. Inevitably some will opt for the minimum. Others like Vintage Property Restoration try to adhere to a code of good practice and insulate whenever they reasonably can. Below I look at some options for wall insulation during restoration projects. In other blogs I look at roof, floor and window insulation.
Cavity wall insulation
In Period Property Manual Care and Repair of Old Houses Ian Alistair Rock defines period property as “a property with solid walls” built before “modern cavity wall construction began” in the 1930s. Interestingly I live a brick period house built before 1900 which does have a thin cavity with was recently filled with cavity wall insulation free of charge and with surprisingly good results. In fact you are always more likely to have a cavity in older brick rather than old stone houses so it is always worth checking.
Cavity wall is by far the easiest, least intrusive and cheapest wall insulation method particularly as you can often get it done free by councils or helpful power companies keen to offset their CO2 emissions and greenwash themselves. If you haven’t got a cavity the options are to insulate externally or internally.
External Wall insulation
Here, insulation boards are fixed to the exterior of the property and then rendered. The big advantage over internal wall insulation is that there is no loss of internal floor space. The major problems are a) it’s a big job that requires fully boarded scaffolding, and b) it can spoil the façade of period properties and may not be allowed in Conservation Areas or on listed buildings.
The photo shows how the attractive features –stone lintels, arches and brickwork – visible on the right hand property are lost after external insulation is fixed to the middle property. To be fair, installation techniques have improved and some of the externally insulated terraces I’ve seen recently have fairly convincing imitation brickwork, cills, lintels and arches reinstated.
Indeed, external wall insulation can be a good option for a lot of 1930s semis and terrace houses particularly when the original render is blown and needs replacing or the brickwork is spoiled beyond repair. It is also worth considering on gable ends and the rear of period properties where the aesthetics may be less important.
Fitting insulation internally can be problematic for two reasons. Firstly, in gentrified period properties with fibrous plaster cornices it cannot really be done without hacking off the cornice on the external walls. It is true that cornices can be rerun or even moved. This is costly, however, and usually only worth doing if the cornice on the exterior walls is damaged anyway. Other period features – picture rail, dada rail, skirting and architraves – are usually made of wood and are fairly easy to relocate or replace.
The second problem is that you lose floor area. This doesn’t have to be a great deal and the thinnest solution is a foil quilt sandwiched between 1” batons. There are thin quilts on the market with a U-value of 0.28 (the equivalent of 100mm of PIR). To baton out exterior walls, I generally use 1” tantalised roofing lat. The foil is stapled to this and then I counter baton with 2”x1” which is then boarded with 12.5mm plasterboard. This gives a total thickness of around 60mm.
Some property restorers would reject the use of multfoils as they wrap walls in a non-breathable membrane. I think the method is suitable for most period properties as long as there are airbricks or other forms of ventilation through the wall to the inside of the foil. To ensure that air can circulate it is important to cut batons short. There should also be ventilation to the inside of the room but this is best achieved by opening windows regularly as having permanently open airbricks is counterproductive.
An alternative method is to “dot and dab” insulation backed plasterboards straight onto the wall. This can be quick if you know what you are doing. People trying it for the first time tend to make a lot of mess, swear a lot, and don’t always end up with very plum walls.
The secret is firstly to put a level on the wall before starting to determine where the plum is running and to identify any bulges. Secondly, you need to mix the adhesive to the consistency of thick icing. It needs to be stiff enough that it will stick on the wall at the desired thickness without sliding but pliable enough that the board can be knocked into plum. Thirdly, you need to dust the wall down with water or, diluted PVA. If you leave masonry dry and dusty the adhesive will stick to the dust and just peel off.
Once the board is positioned, test for plum and line and knock into position with a block and hammer. If part of the board refuses to stick just put in a rawl plug and screw a baton over the lose area. The screw can be tightened and loosened to bring the board into plum.
Dot and dab is a good solution if the ceiling height is eight foot or under (the length of a standard wall board). If you use tapered edged boards, the joints can be just taped and filled, the corner between wall and ceiling caulked and the wall can be painted with no need for skimming. As with the multifoil it is good practice to ensure that there is adequate ventilation through the wall to the inside of the insulation.
There are 4mm thermal wallpapers available. These will not achieve anything like the U-value of boards or foil though they are better than nothing and many people say that they achieve noticeable results. They are a particularly handy option if you have decorative cornices and skirtings you want to conserve or if you cannot afford to lose any floor space.