Loft insulation in Spetisbury

Air first, because the order matters. Insulation is carried across the ceiling until it sits over the wall plate and it stops there, with a vent tray at each rafter holding an air gap open above it. That gap is the route: cross ventilation moves from one eaves, along under the felt and out the other side, taking vapour with it. Where a roof has boxed soffits that cannot be opened, a ridge vent or a run of tile vents does the same work from higher up, and a modern breathable membrane changes the detailing rather than removing the need. Approved Document F is the standard behind it. Get this right and the loft stays dry however cold it gets. Get it wrong and the dew point sits inside the material, interstitial condensation forms where nobody can see it, and black mould appears on the rafters within a winter.

The hatch belongs to the same argument. A bare trapdoor in an untreated lining is the main way warm wet air leaves the house and enters the roof, so it takes a rigid board on its back and a compression seal round the lining before any depth is discussed. Extract fans in the bathroom and kitchen are worth a look at the same time, because a fan discharging into the loft instead of out through the wall will defeat everything else in this list.

Only then the depth. Whatever is there now gets read first: it will have settled, gone patchy, been compressed under storage and stopped short at one edge, and if it is damp, dusty or contaminated with droppings it is bagged in place and carried out. Sound wool stays as the base layer, teased apart and levelled between the joists. Over it goes the second layer, cross laid across the joists at right angles so the timber is buried and stops carrying heat down into the plaster. About 270mm finished is the depth a renovated ceiling is expected to reach under Part L in Approved Document L. Mineral wool roll on the open floor, rockwool batts where the bays vary, glass wool, loose fill in the corners, sheep wool if you prefer it, PIR rigid board and multi-foil where the headroom has gone.

Then the fittings, quickly, because they are easy to leave out. Fire rated covers over recessed lights and downlighters. Cable and wiring lifted onto the new layer rather than buried under it. Lagging on the cold water tank and its pipework, which are now sitting in genuinely cold air. Loft legs and a raised floor where you want storage, so the boarding and the platform clear full depth, with the loft ladder set to suit. And where a roof has already been converted into a room in roof, the whole approach changes to a warm roof at rafter level, with a taped vapour control layer behind the plasterboard and the sloping ceiling and dormer cheeks treated as carefully as the flat part.

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 terraced cottage with a small trap over the stairs, a semi with a landing hatch and a fitted ladder, and a house with the loft already boarded and full are three quite different starts to a day. 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.

There are two clearly different sorts of roof along this stretch, and they want different things. A fifth or so of the houses are pre-war cottages with cut roofs, purlins through the space, hand cut joists at spacings that wander, and often no underlay at all. The larger share went up between the war and the early eighties, mostly semis and terraces with trussed roofs, a sealed underlay and one thin quilt rolled out when they were built.

On the older roof the ventilation is largely a gift and the difficulty is fitting material to a space where no two bays match, which means batts and cutting rather than rolling. On the later roof it is the reverse: the floor is regular and easy to cover, but the roof is sealed above and the original layer has usually been shoved into the eaves, so the air path is the thing that needs rescuing. Ask anybody quoting which of the two you have and what they intend to do about it. If the answer is the same for both, they have not been up there.

We cover Spetisbury, Charlton Marshall, Blandford St Mary, Blandford Forum, Sturminster Marshall 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.