Wall insulation in Crossways

The survey, short as it is. Newer stock does not mean no survey. The camera settles the width, whether the cavity is clear, whether the inner leaf is dry and whether partial fill boards are already fitted against it. It takes ten minutes and it costs nothing.

Bonded bead. Polystyrene bead blown in with adhesive so it binds and stays put. It flows past obstructions, gets into a narrower gap and sheds water rather than holding it. It is the right choice on anything exposed and on anything under about 70mm.

Blown mineral wool. A good, cheaper option in a wide, clean, sheltered cavity, and there are plenty of those in Crossways. Its one weakness is water: where driven rain crosses the gap the fibre holds it against the inner leaf, so it is not for a weather facing gable.

Houses built with partial fill. From the mid 1970s a lot of Crossways builders fixed rigid boards against the inner leaf and left a clear gap in front. Blowing loose fill into that gap bridges it and can produce damp where there was none. The camera tells us which sort you have before anything is ordered.

The walls we still turn down. A wet cavity, one full of rubble at the base, one bridged with mortar, or a wall with no cavity trays over the windows. A fill in those buys a little heat loss back and a lot of penetrating damp risk.

Solid walls and extensions. In Crossways, the odd older cottage, a single skin garage conversion or a room over a porch has nothing to fill. Those take internal wall insulation, insulated plasterboard or PIR such as Celotex or Kingspan on a batten or stud frame with taped joints and a continuous vapour control layer, or external wall insulation with a mesh basecoat and a render carrier over the top.

Reveals, thresholds and junctions. A filled Crossways cavity still leaves cold bridges round the openings, at the threshold, along the floor junction, at the eaves and at the joist ends. Those strips are where condensation and black mould arrive. Shallow reveals take an aerogel laminate. This is the slow work and the first thing a cheap quote loses.

Ventilation and old fill. Trickle vents, extract fans that shift air and air bricks left clear, to the rates in Approved Document F. Where a 1980s fill has slumped and left the top metre empty, or the cavity is wet, it has to be extracted and the wall dried before refilling makes sense.

Before anything else, Thomas establishes what kind of wall you have. He drills one small hole and looks into the cavity with a borescope to see if it is clear, empty or already filled, and checks how exposed each wall is to driven rain.

Then he prices it himself. The quote itemises the survey and borescope, the fill or system and its thickness, making good at windows and doors, ventilation works and disposal. A fill should come from a registered installer with a CIGA certificate.

The bulk of Crossways was built with a brick outer leaf, a cavity and a block inner leaf, mostly in the seventies and eighties. Many can be filled from outside through small holes that are then made good to match. Some were filled years ago, and older fill can slump or get wet, leaving cold patches. The older cottages in the village have solid walls and need a lining instead. Cavity fill is done from outside with the openings sealed; internal lining is done room by room, with furniture moved and floors sheeted. Waste leaves with us each day. If the borescope shows old fill that is wet, you get a photo and a price for taking it out before anything is added.

Nobody controls the look of the outside here, as Crossways has neither a conservation area nor a listed building. External work is still worth checking against the rules on external walls, and internal insulation is not development, as the insulation guidance explains. Building control engages through regulation 23 once more than half a wall is renovated, under Dorset Council.

If an outside wall shows damp or black mould after it was filled or lined, either water is crossing the cavity or warm air is hitting a cold junction. If the fill went in years ago, tell us roughly when, because older mineral wool and bead fills behave differently from what is installed now.

Note whether the patch is on the weather side of the house and whether it dries out in summer. We find the cause on the first visit before removing anything, and it can turn out to be a gutter or pointing fault, not the fill. Scheduled work is Monday to Friday, 8am to 6pm. If damp is spreading, ring instead of using the form, and missed calls are returned as soon as we can.

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Much of the country round here is old, protected, or both. Crossways is neither. The village grew from the 1970s onwards, there is no conservation area over it and there are no listed buildings in it, so neither of the usual planning complications applies to a wall job. You do not need permission, the finish is your choice, and the walls were built with a cavity in mind.

That changes the conversation in a useful way. In a cob or flint village most of a survey is spent explaining what cannot be done. Here it is spent on which fill and on the reveals. A cavity fill on a house like this is a day's work from outside, nothing to move indoors, no scaffold on a bungalow, and the shortest payback of anything we do. Part L sets what the finished wall should reach and a modern cavity comfortably gets there.

What needs care here is related to age. Houses built from the mid 1970s may already have partial fill boards in the cavity, and blowing more in on top of those is a way of making damp. And a fill installed in the 1980s may have slumped since. Neither is a reason to avoid the work, both are reasons to put a camera in first. We do not run a guarantee scheme of our own. A fill by a registered installer normally carries a CIGA certificate, so keep that with your EPC.

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

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