Wall insulation in Redlynch

Deciding what the wall is. Reveal depth, brick bond and the sound it makes when tapped give the first answer, and a borescope through one drilled hole in a mortar joint gives the real one. Where a later extension or a post-war house does have a cavity, the same camera shows whether it is clean, dry and wide enough to take a fill.

Cavity fill where there is a cavity. In Redlynch, bonded bead suits a narrow, obstructed or exposed brick and block wall; blown mineral wool only in a wide, clean, sheltered one. Drilled from outside, filled, holes pointed to match, one day. It is the shortest payback of anything we do to a wall, and Part L sets what the finished wall should reach.

What breathable actually means. Not draughty. On a Redlynch wall it means the build up lets water vapour pass through instead of trapping it, so moisture that gets into the masonry can leave again. Wood fibre board bedded and finished in lime does that. A foil faced PIR board taped tight to the wall does the opposite, and on a pre-1900 wall that is how you rot the joist ends built into it.

Internal wall insulation, done for an old wall. Wood fibre in lime, or a lime based insulating plaster where the wall is uneven, fixed against a wall that has been allowed to dry first. Where the wall is modern and sound we do use insulated plasterboard or PIR such as Celotex or Kingspan on a batten or stud frame with taped joints, because there the vapour control layer is the right answer. Different walls, different build ups.

Where the dew point ends up. This is the whole argument. Insulate the inside of a Redlynch wall and the masonry behind gets colder, so the point at which vapour condenses moves into the wall. A breathable build up lets that dry out. A sealed one holds it, and interstitial condensation inside a wall is invisible until the skirting goes soft.

External wall insulation. On a Redlynch house EWI keeps the masonry warm and dry and removes the thermal bridge at the eaves and the joist ends, and with a lime or mineral render carrier it can be done breathably. It costs more and it changes how the house looks, but on the right building it is the better engineering answer.

Reveals, floors and junctions. The reveals, the threshold, the floor junction and the joist ends are the cold bridges and the damp risks together. Shallow reveals take an aerogel laminate. Joist ends in a solid wall get a detail that keeps air moving round them rather than burying them in insulation.

Air, and putting failures right. An old Redlynch house that has been sealed up needs trickle vents, working extract fans and air bricks kept clear, to Approved Document F. We also strip out linings that have failed, extract slumped or wet cavity fill and dry the wall before anything else goes near it.

Thomas first works out which walls you have. A post-war house is likely to have a cavity, while a cottage built before the First World War usually has solid brick or flint. Where it is not obvious, he drills one small hole and looks in with a borescope. The quote itemises the survey, the system and its thickness, making good round windows and doors, ventilation, and disposal. Any cavity fill should come from a registered installer with a CIGA certificate.

Cavity fill is drilled from outside, from a ladder or tower on a bungalow and scaffold on a taller gable. Internal lining is done room by room, so furniture is moved, floors are sheeted, and old plaster leaves with us. On solid walls we use breathable materials, such as wood fibre board and lime plaster, so moisture can still get out. Damp, a rotten skirting or a problem inside the cavity gets photographed and priced, and the work pauses until you have said yes.

Wiltshire Council is the planning authority. With no conservation area over Redlynch, inside work is simple, but external insulation should be checked against the rules on external walls. A listed cottage needs consent for internal work too, under section 7 of the 1990 Act. Building control comes in through regulation 23 once more than half a wall is renovated.

If damp patches or black mould have appeared on an outside wall after it was filled or lined, ring; the form is slower. It usually means rain is bridging the cavity, or warm air is reaching a cold spot at a junction.

On a solid cottage wall, a lining that does not breathe can trap water behind it. The first visit finds which it is before anything is removed, and ventilation can often be improved on that same visit. If there is a lining, tell us roughly how old it is and what it is made of. Scheduled work runs Monday to Friday, 8am to 6pm. If you cannot reach us, we will ring you back.

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Plenty of the housing in this parish predates 1919, and some of it is much older still. Those walls are solid, they were built in soft brick or rubble bedded in lime, and they have survived a century because water can get out of them as easily as it gets in. Every decision about insulating one follows from that.

In practice it means lime and wood fibre, not foam and foil. Getting the wall dry before anything goes on it, which usually means the ground level, the gutters and the pointing rather than anything clever. And accepting a slightly worse U value in exchange for a wall that is still standing in thirty years, because the thinner, tighter build up that looks better on paper is the one that traps moisture.

The honest advice on a lot of these cottages is that the walls are not where your money should go first. Loft insulation to full depth, sealing the draughts round doors, floorboards and the chimney when it is not in use, and heavy curtains, all cost a fraction of a lined wall and cut more of the heat loss you actually feel. When somebody quotes you for wall insulation without asking what is in your loft, that tells you something.

Nearby places we also cover for wall insulation, with straight-line distances from Redlynch, and the other trades we offer in Redlynch itself.

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