Wall insulation in Winfrith Newburgh, from the base up

The borescope, before anything else. One small hole in a mortar joint, a camera in, and the argument is over. It shows whether there is a cavity, how wide it is, whether the leaves are bridged with mortar droppings and whether the inside face is wet. Nobody should write a quote for wall insulation without it.

Cavity fill, and the two materials. Bonded polystyrene bead is blown in with an adhesive, flows into a narrow or partly obstructed cavity and does not slump afterwards, which is why it suits older brick and block walls here. Blown mineral wool is fine in a clean, wide, sheltered cavity, but it holds water if driven rain crosses the gap, so not on an exposed south west elevation.

When we say leave it empty. A cavity under about 50mm, one full of rubble, one already wet, or a wall with no cavity trays over the openings. Bridging a wet cavity carries water to the inside face, and that is the commonest reason damp appears on a wall that was dry before.

Solid walls. A nine inch brick wall, a cob wall or a flint and rubble wall has nothing to fill. It gets lined inside or insulated outside. Before either, the wall has to be able to dry: ground level down, gutters running, joints sound.

Internal wall insulation. Insulated plasterboard, a PIR board such as Celotex or Kingspan, fixed to a treated batten or a stud frame with taped joints and a continuous vapour control layer. On an old solid wall we more often use wood fibre finished in lime, so the wall keeps drying inwards. Rooms lose 60 to 100mm and every socket and skirting comes off and goes back. BS 8000-8 covers the drylining.

External wall insulation. Board fixed to the outside, a mesh reinforced basecoat, then a silicone topcoat or a render carrier and a finish to match. It keeps your room sizes and puts the whole wall on the warm side, giving the best U value of the three, but it changes how the house looks, so here it is a planning question first.

Junctions, where the money and the mould both are. Reveals at windows and doors, the floor junction, the eaves, the joist ends built into the wall and any party wall. Those are the cold bridge points, and an insulated wall with a bare reveal just moves the condensation to the reveal. Thin aerogel laminate gets insulation into a narrow reveal without losing the window.

Ventilation and failed fill. A tighter wall needs somewhere for moisture to go: trickle vents, a real extract fan in the kitchen and bathroom, air bricks kept clear rather than covered, to the rates in Approved Document F. And where old fill has slumped and left the top metre empty we extract it, dry the wall and say honestly whether to refill.

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.

Insulating the inside of a wall is not development, which the Planning Portal's guidance on insulation confirms. Winfrith Newburgh has its own conservation area, so external wall insulation there changes the appearance and needs an application; Dorset Council holds the record of what is designated. Building control does engage, because regulation 23 brings a wall up to current standard once more than half of it 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. Tell us whether the damp arrived after the wall was insulated or was always there, because that one answer changes where we start looking. The phone is answered 24 hours for emergencies; scheduled work runs Monday to Friday, 8am to 6pm.

Call now: 07435 839745

The Win runs through the village and the low ground either side sits in the higher flood zones, which you can check for any address on the government's flood risk service. For walls that matters in one specific way, and it is not about flooding.

Ground that stays wet keeps the base of a wall wet. In the older cottages the outside ground level has crept up, the floor inside sits low, and there is either no damp course or a slate one that has been bridged. Line a wall like that with a vapour tight board and you seal the moisture in. The wall stops drying inwards, the joist ends sit wet, and mould appears along the skirting within a winter. BS 5250 is the code of practice for it, and interstitial condensation behind a lining is far harder to see than the surface kind.

So on the wet side of the village the dull work comes first: ground away from the wall, gullies clear, a reading that has stopped moving. Then a breathable lining. Where the base of a wall will not dry at all, the honest answer is to leave it and put the money into the loft and the draughts, which will do more for the heat loss anyway.

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