Loft insulation in Post Green

More than half the houses here went up between the war and the early eighties, which means a great many trussed roofs. A truss roof is a lattice of thin timbers braced against one another, and it is not a space you walk about in. Access is the hatch and nothing else, so everything is fed in from there and worked outwards, bay by bay, on crawl boards that move along with you. It is work at height from the moment the ladder goes up. The middle is quick. The last couple of metres into each corner take as long as all the rest put together, and that is the part a cheap quote quietly leaves out.

Depth goes in as two layers. The first sits down between the joists. The second is laid across the top of them at right angles so no timber is left showing, because a bare joist takes cold straight through into the bedroom underneath. Finished, the two come to about 270mm and the Approved Document is where that figure comes from. Rolls of mineral wool do the long runs, batts drop neatly into the small bays a truss creates, loose fill can be poured where the pitch is too shallow for anything else, and sheep wool is an option if you would rather not have glass wool or rockwool above your head. What you are actually buying is a lower U value across the ceiling, which is the largest single piece of heat loss in most houses and the one that shows on the heating bill and on an EPC.

Airflow is the other half of the job, and on a 1970s roof it is usually the half that has gone wrong. The wool has to stop dead on the wall plate so the air gap above stays open, and vent trays clipped between the rafters keep it open when somebody later pushes a suitcase into the eaves. Cross ventilation starts at that gap. It runs up the slope and escapes under the ridge, quicker where a ridge vent is fitted. Where the underlay is old bitumen felt rather than a modern breathable membrane there is no second chance, because felt lets nothing through it. Insulating the ceiling drops the temperature above it and takes the dew point with it, and a blocked eaves then turns into condensation, wet wool and black mould on the timbers within a season.

The rest is housekeeping that pays for itself. Anything up there that has gone patchy, settled to half its thickness, been compressed under a floor or contaminated where birds have left droppings comes out, along with whatever is missing at the edges. It is bagged where it lies and taken away rather than buried under the new. The cold water tank gets lagging, and its pipework with it, because the loft is about to become a much colder place than it has been. Wiring and cables are lifted onto the wool instead of trapped beneath it. Fire rated covers go over recessed lights and downlighters. Storage does not have to be given up: loft legs go on first, the boarding is refitted at the higher level, and the ladder is trimmed or reset so it still meets the platform, with a board and a seal on the hatch to finish. Close to a third of the homes here are bungalows, where all of that work sits over every room in the house rather than half of them.

Where a room has been built into the roof there is no floor to lay on and the job moves up to the rafters. Rigid board, PIR or Celotex, is cut tight between them, an air path is kept clear above so the timbers can still dry, a layer goes under the rafters, and the room side is closed with taped vapour control. Multi-foil quilt is for a sloping ceiling or a dormer cheek that can give up nothing. Get the vapour side wrong and the moisture goes interstitial, sitting inside the build up rather than on a surface where you would see it. Where the covering is coming off anyway, a warm roof over the deck is the better answer.

No rate per square metre, because the floor area is the easy part and the awkward edges are where the time goes.

Getting to it. A 1970s bungalow with a landing hatch, a semi with a small hatch over the stairs, and a detached house with a fully boarded loft are three different mornings before any material is opened. A hatch on a landing you can stand a ladder under is one job. A hatch over a stairwell, a crawl space you can only move through on your knees, or a loft full of boarding that has to come up and go back, is time before any material is laid.

What is up there now, and what it is sitting on. Old material that has to come out, be bagged and taken away is a cost before anything new goes down, and so is a loft full of boxes that has to be emptied and put back. Joists at 400 centres with a flat run across them is a different afternoon from a trussed roof full of bracing.

Ventilation, and the edges nobody reaches. Insulation stops at the wall plate and the eaves have to stay clear, or you trade a warm bedroom for a wet roof. Getting depth right into the corners and around the hatch, boxing over downlighters and lagging anything that now sits in the cold, is most of the labour. Approved Document L sets what the work is expected to reach.

Comparing quotes? Ask what depth is actually being laid and in how many layers, whether the old material is coming out or being covered over, whether the eaves are being kept clear, what happens to anything you store up there, and whether the hatch and the pipework are included. Two quotes for the same job are usually two different jobs.

We cover Post Green, Lytchett Minster, Upton and the BH16 addresses around them, with Dorset Council for planning and building control. You are dealing with Bournemouth Roofing & Building, the trading name of Bournemouth Roofing & Building Ltd, registered in England and Wales, company number 15471719, which you can look up in a minute. Thomas Hannen's business, and he is the one who comes out to price the job, not a salesman. A verified customer's 10 out of 10 on Checkatrade. The visit and the written quote are both free.