Wall insulation in Redlynch, on walls that breathe

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. Bonded bead for 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. It means the build up lets water vapour pass through rather than 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 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. 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 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.

Same team from first visit to last, one person to ring, and no sub-contracting your work out to somebody you have never met. The quote is itemised, not a figure on the back of a card: the survey and any borescope check, the system and its thickness, making good around windows and doors, ventilation works, and disposal on separate lines, so you can compare it properly against anyone else's.

Nothing is left open or unusable overnight. The site is swept at the end of each day rather than the end of the job, and what comes out leaves with us. If something turns up once we start that nobody could have seen, you get a photograph and a price before we carry on.

Wiltshire Council is the planning authority for Redlynch. There is no conservation area over the village, so internal insulation is straightforward and external work is worth checking against the rules on external walls first; a listed cottage needs consent for internal work as well, under section 7 of the 1990 Act. Building control engages through regulation 23 once more than half a wall is renovated.

Ring rather than use the form. Damp patches or black mould appearing on an outside wall after cavity fill or internal lining usually means water is tracking across the cavity, or warm air is reaching a cold surface at a junction. We look before we take anything out, because the fix depends on which of those it is. If a lining is already on the wall, tell us how old it is and whether anything was taped behind it, because that decides whether we can leave it in place. The phone is answered 24 hours for emergencies; scheduled work runs Monday to Friday, 8am to 6pm.

Call now: 07435 839745

Something over a quarter of the housing in this parish predates 1919, and most of that is 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 three things. Lime and wood fibre rather than 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.

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