Our expert advice for solving your project dilemmas

Planning a project? Our Real Homes expert, Jason Orme, solves all of your home transformation dilemmas

Q: I’ve just bought a pre-war detached house and it’s proving colder than I’d expected. What’s the best way to improve it?

A:

Insulating the roof and walls are the most sensible priorities and the easiest to achieve. In terms of the roof, you will want to ensure that the floor of the loft has at least 270mm of mineral wool insulation. It’s highly unlikely that this is the case – even if the loft has been insulated, the wool will have been padded down over the years (people put suitcases and all sorts of things on top of them) and, as a result, be less effective. Installing it is a DIY job, but you’ll need to make sure you wear protective clothing and masks as the wool can be an irritant. If you want to use the loft for storage, then you could consider using loft legs that enable you to fit a floor over the insulation.

Next it’s the walls. Ideally, external insulation is the best bet as it provides a warm wrapper around the house and moves the dewpoint to the outside of the internal walls. However, that does mean disrupting the home’s existing external appearance, so it isn’t for everyone. If that’s the case, the easiest solution is to fit insulated plasterboard, which is regular plasterboard with an insulation layer bonded on the rear face. This can significantly reduce heat loss through your walls and is the best option for those looking to improve performance without losing too much in the way of floor space – the plasterboard is 27mm or 55mm thick, depending on how much you want to insulate, compared to the usual 12.5mm.

It is pretty expensive – around five times the price for the thinner version, up to 10 times the price for the thicker board. Just think of all those warm nights on the sofa you’ll be enjoying though.

Q: What construction system should I use for my extension?

A: The method of building walls for those building their own homes varies significantly, but the same choice hasn’t affected the home extension market yet. It is, however, slowly changing. The usual solution is the cavity wall, which consists of an outer skin of brickwork (or blockwork rendered or clad in timber) and an internal skin of masonry blockwork. In between, there is a cavity, usually a 100mm gap which is filled, either partially or fully, with insulation.

This is still the standard way to build walls, and it’s very effective. As energy performance standards for walls have changed in recent years, the cavity required has increased with the thickness of insulation, giving builders the option of reducing heat loss. The thickness of that external wall can hit 350mm. When garden space is limited, this can be significant space lost.

Extenders in these situations might like to consider a timber frame or Structural Insulated Panel system (SIPS), where the insulation is set as an integral part of the walling (in timber frame, between the 89 or 140mm studs; in SIPS, as the core between two outer sheets of OSB, achieving similar thickness). These walls can then be clad or rendered on the outside – or a brick slip system used. The systems will achieve excellent energy performance and, compared to cavity walls, might save over 100mm on the overall thickness – which, around the whole extension on a tight site, could equate to an extra 3-4m2 of added space.

There are many other excellent systems, not least Insulated Concrete Formwork (ICF) which is a kind of masonry SIPS system in reverse, with a poured concrete core separating two layers of insulation. All differ slightly in terms of cost, but with the exception of wall thickness, the differences between the systems are probably not sufficient to justify changing your builder, or their preferred system, to suit.

Q: My architect has designed a flat roof for my extension, but I’m worried about it leaking. Should I be?

A: In a word – no. Flat roofs are not what they were in the 1960s and 1970s, when they were effectively felt roof with loose chipping covers over a simple deck, built totally flat, ready for puddles to form. These days, many flat roofs are built as so-called ‘warm’ roofs, where a thick layer of rigid insulation sits above a vapour barrier and is covered by either a single-ply or fibreglass/ rubberised layer. These single ply systems tend to come with a 20-year guarantee and are expected to last for decades longer – they don’t tear and are resistant to extreme heat and cold.

Crucially, it is important to ensure that your designer has allowed for a fall on the roof level itself – 2-4˚ should be sufficient. This can be achieved through pre-formed firring strips (they can also be built on site). The installation of your roof cover is best left to a specialist roofing contractor with experience in the application of these new systems.

Q: I’d like to have my patio on the same level as the flooring on the inside of my extension, but my builder says it’s difficult to do well. Are they right?

A: They are, but it’s not impossible. It depends on that all important building commodity – teamwork.

Your builder will need to plan for it in the floor construction, because the installation of a dedicated drainage system will ensure any rainwater is channelled away from the inside. It should go without saying that a level threshold also makes the light fall in the patio all the more important – away from the house, obviously. The other part of the equation is in terms of the track detail, which is down to the sliding door manufacturer – and there are various solutions offered by the main providers. Because the frame itself disappears in a system like this, the problem is often on the kicker seal of the doors, which needs to be carefully detailed as it can be a bit leaky in terms of air getting in and out. Look out for systems that are weather rated. You also might want to create mitigating design factors such as an overhang to ensure that weather is not constantly battering the door. Lastly, if you can’t satisfy yourself or your builder as to the weather rating of the supplier’s level threshold system, then consider a low threshold instead – it provides the same visual effect, with none of the potential problems.