Loft insulation in Post Green

Much of the housing in Post Green 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 into a Post Green loft 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 one of the larger pieces 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 in a Post Green loft, 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. In a bungalow, and there are plenty here, all of that work sits over every room in the house, not half of them.

Where a room has been built into a Post Green 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.

Area and pitch set the time. A Post Green bungalow loft is big, and a low pitch means lying flat to reach the eaves. Getting full depth tight into those edges takes most of the time.

The way in. A hatch on a landing with room for a ladder is quick. A tiny hatch in a narrow hall, or a floor boarded for storage that has to be lifted and relaid, adds hours before any wool is unrolled.

What is up there already. Old wool that has flattened or got damp is bagged out, and stored boxes are moved and put back.

Keeping storage. To store things above the new depth, boards go on raised legs. Boarding laid straight on top crushes the wool and wastes it.

Pipes and cables. Wiring is lifted above the insulation, the cold water tank and pipes are lagged, and recessed lights get covers so they stay cool.

Air at the eaves. Blocked eaves mean condensation on the felt, so trays or vents are part of the job. Approved Document L sets the target the work is measured against.

Ask anyone else how deep and in how many layers, whether the old wool comes out, and whether the eaves are being kept open.

About nine and a half miles separates Post Green from our base in Boscombe. Lofts in Post Green, Lytchett Minster, Upton and the BH16 addresses around them are all ones we cover, and the authority for planning and building control is Dorset Council.

You deal with Bournemouth Roofing & Building Ltd, registered in England and Wales, company number 15471719. Thomas Hannen runs it and goes up the ladder to price the loft himself. A verified customer's score on Checkatrade is 10 out of 10. Neither the visit nor the itemised quote in writing costs anything. Before you book a visit in Post Green, you can read our customers' Google reviews, word for word, on our reviews page.

Most repairs in Post Green need no application at all. What decides whether a change to the outside of your house does is who the council is, whether a conservation area or a listing applies, and whether the place sits in a protected landscape.