Loft insulation in Iwerne Minster

Nothing in a cut roof repeats. The rafters were pitched on site with purlins running through the middle of the space, so you can stand up in most of it, but the ceiling joists below were cut by hand and their spacing wanders from one end of the run to the other. Roll does not like that. It bridges the narrow bays and leaves a gap in the wide ones, so the first layer usually goes in as rockwool batts or as mineral wool roll cut to each bay, friction fitted tight to the timber on both sides. Where the joists sit close together and there is no room to open anything out, loose fill poured in and levelled does what a roll cannot.

What we find first is rarely bare timber. Something went down decades ago, and by now it is compressed flat wherever anyone has knelt, patchy across the middle, missing altogether along one side and full of holes where a cable or a pipe crosses. Sound wool is worth keeping: it gets teased apart, straightened between the joists and covered. Anything contaminated with droppings, anything wet under a slipped tile, and granular fill drifted into the corners is bagged where it lies and carried out.

The ceiling under all this is often lath and plaster, and lath and plaster will not take a knee. So the work runs off boards spanning the joists, moved along as we go, and material is carried out from the hatch rather than dragged across the tops of the timbers. Where the roof drops away over a back addition the space becomes a crawl, and that stretch is measured in time rather than in floor area. Getting up there is work at height even indoors, so the ladder and the hatch are settled at the survey and anything you store up there comes down before we start.

With the base even, the second layer goes on and it runs the other way. Cross laid over the top of the joists instead of between them, so the timber is buried and stops carrying heat straight down into the plaster. That is the layer people leave out, and it is the one that moves the U value. Two layers to about 270mm is what a renovated ceiling is expected to reach under Part L, set out in Approved Document L, and on a house with solid walls it is the cheapest thermal work left in the building. Glass wool, rockwool, roll or batt, sheep wool if you would rather have a natural fibre: the choice comes from the shape of the loft, not from the label on the packet.

Then the perimeter and the fittings, which is where the hours actually go. Insulation is carried out over the wall plate and stopped there, with a vent tray at every rafter holding an air gap open so cross ventilation still runs soffit to soffit. Choke that gap and the dew point moves into the structure, interstitial condensation forms on the underside of the felt where nobody can see it, and black mould creeps down the rafters by the end of the winter; BS 5250 is the code that deals with moisture in a roof, and it is worth knowing that the risk is well understood rather than bad luck. A ridge vent or a run of tile vents takes the job on where the eaves cannot be opened, and a breathable membrane changes the detail rather than the requirement. Recessed lights take fire rated covers. Every cable is lifted and clipped above the new layer instead of being buried in it. The cold water tank and its pipework get lagging now they sit in properly cold air, with nothing laid underneath the tank. The hatch has a board fixed to its back and a draught seal round the lining, loft legs carry a raised floor if you want to keep using the space, and the loft ladder is checked against the new height. Where the roof was turned into a room years ago the job moves to the rafters instead: PIR rigid board such as Celotex cut between them with the air gap kept above, a taped vapour control layer behind the plasterboard, and multi-foil quilt in the sloping ceiling and the dormer cheeks where there is no depth left to give.

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 cottage with the hatch over the stairs, an older house with purlins in the way, and a modern detached on the edge of the village are three different jobs. 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 Iwerne Minster, Fontmell Magna, Child Okeford, Shillingstone, Blandford Forum and the DT11 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.