Wall insulation in Cranborne
The conservation area rules the outside of the wall out, so the answer here is a lining that lets the old masonry go on drying inwards.
The site visit is free and so is the written itemised quote. Thomas Hannen prices every job himself.
In Cranborne the external route is effectively closed. Wrapping a house in insulation and render changes the appearance of the building, and inside a conservation area that is an application rather than a given. So on the older walls the job moves indoors, and the whole question becomes how to line a wall without stopping it drying.
People ring about a cold front room, about mould behind furniture on an outside wall, or because they have been quoted for insulated boards and want to know whether that is safe on a building of this age. It is a fair question and the answer is not always yes.
We come and look at the wall itself. Thickness, what it is built of, whether it is brick, flint and brick banding or a rubble core, how the render or the pointing is behaving, and where the floor joists are bedded into it. On the newer houses one drilled hole and a borescope settles whether there is a cavity worth filling. Then you get a written itemised quote with the survey, the system, the junctions and the ventilation on separate lines. The visit and the quote are free.
On these walls
Lining an old wall so it can still dry
Working out what you have. A nine inch solid wall, a thicker rubble or flint wall and a brick and block cavity wall all look similar once they are rendered. A borescope through one hole tells us which, and whether a cavity is clear, dry and wide enough to take a fill at all.
Breathable internal wall insulation. On a solid wall of any age the safe build up is vapour open: wood fibre board bedded in a lime mortar and finished in lime plaster, or a similar capillary active system. Moisture that gets into the wall can still travel and leave. There is no plastic sheet trapping it at the back of the board, which is the mistake that causes trouble later.
Where a rigid board is right, and where it is not. Insulated plasterboard, or PIR board such as Celotex or Kingspan between battens or a stud, is quick, thin for the performance and entirely correct on a modern wall or a dry, hard fired brick one. On a soft, damp or rubble filled wall it seals the inside face, and the moisture that used to evaporate into the room stays in the masonry.
The junctions. Reveals, the threshold, the floor junction and the joist ends. Timber built into an old wall is the detail that matters most, because a lining makes the wall around those joist ends colder and wetter than it was. We keep the ends ventilated rather than boxing them in. Where a reveal has no depth, a thin aerogel board goes in rather than nothing.
Cold bridges. A lining that stops at a party wall, a chimney breast or a ceiling makes a thermal bridge at that line, and a thermal bridge is where the dew point lands and black mould turns up. Returns and overlaps are drawn at the survey rather than improvised on site.
Cavity fill on the newer houses. Bonded polystyrene bead, or blown mineral wool on a sheltered wall with a sound outer leaf, blown through a drilled pattern with the holes made good in a matched mortar. A house is normally a single day.
Failed fill and ventilation. An old fill that has slumped, or wetted up through cracking render, comes out through drilled holes and the wet cavity is dried first. Then trickle vents, a working extract and air bricks kept clear, because Approved Document F expects a tighter house to still lose its moisture somewhere.
How it runs
From your call to a written price
Same team from first visit to last, one person to ring, and no sub-contracting your work out to somebody you have never met. The quote is itemised, not a figure on the back of a card: the survey and any borescope check, the system and its thickness, making good around windows and doors, ventilation works, and disposal on separate lines, so you can compare it properly against anyone else's.
Nothing is left open or unusable overnight. The site is swept at the end of each day rather than the end of the job, and what comes out leaves with us. If something turns up once we start that nobody could have seen, you get a photograph and a price before we carry on.
Dorset Council is the planning authority and the village sits in the Cranborne Conservation Area, where external appearance is controlled, so the council's heritage pages are the place to start on any external system. There are 25 listed entries around the village, Cranborne Manor House among them, and on a listed building consent covers internal work too. Lining the inside of an unlisted house is not development, which the Planning Portal confirms. Building control comes in under regulation 23 once a thermal element is renovated, and Part L sets the U value.
Cost
What decides the price of a wall insulation job
No rate per square metre, because the wall area is the easy part; what happens at every window, door and floor junction is not.
Getting to it. A thick walled cottage on the square, a rendered house on the lane and a modern infill with a proper cavity are three different jobs before anything is drilled. Cavity fill is drilled from outside and a bungalow comes off a tower where a three storey gable wants a scaffold. Internal lining is worked room by room from inside, so it is your rooms rather than a platform that gets disrupted. The work at height rules still set the platform.
Which wall you actually have. A cavity that is clear and dry can be filled in a day. A solid wall cannot be filled at all, and has to be lined inside or insulated outside, which is a different job at a different price. A borescope through one drilled hole settles it, and no honest quote is written before that.
The junctions, not the field of the wall. Reveals at windows and doors, the floor junction, the eaves and any party wall are where heat escapes and where condensation shows up if the detailing is wrong. That work is slow, it is most of the labour, and it is the first thing a cheap quote leaves out.
Comparing quotes? Ask whether the wall has actually been checked with a borescope or just assumed, what system and what thickness is specified, how the reveals and floor junction are being detailed, whether ventilation is being addressed, and who makes good the plaster and decoration afterwards. Two quotes for the same job are usually two different jobs.
If damp has appeared
Damp or mould after a wall was insulated
Ring rather than use the form. Damp patches or black mould appearing on an outside wall after cavity fill or internal lining usually means water is tracking across the cavity, or warm air is reaching a cold surface at a junction. We look before we take anything out, because the fix depends on which of those it is. On an old wall we want to know how long the patch has been there and whether it dries out in summer, because that tells us where the water is coming from. The phone is answered 24 hours for emergencies; scheduled work runs Monday to Friday, 8am to 6pm.
Worth knowing
Why the answer moves indoors here
A conservation area is about how the place looks. External wall insulation adds a hundred millimetres or more to every elevation, buries the sills and the eaves detail, and replaces the face of the building with render. On a village street of brick and flint that is a change of character, and it is the sort of application that is refused rather than granted.
That leaves the inside face, and it changes the engineering completely. Insulating outside keeps the masonry warm. Insulating inside makes it colder, because the heat that used to reach it no longer does. A colder wall holds more moisture and dries more slowly, and if you have also sealed the inside face with foil backed board and a vapour barrier, the water that used to evaporate into the room has nowhere left to go. That is how interstitial damp and rotten joist ends start.
So on a wall of any age here we build the lining vapour open, in wood fibre and lime rather than plastic and foil, and we manage the ventilation at the same time. It is a slower and more careful job than screwing boards to a wall. Heat loss through the walls is usually the largest line on the EPC of a house like this, so the payback is real, but it only holds if the wall stays sound.
Who you are dealing with
A local firm you can check
We cover Cranborne, Alderholt, Wimborne St Giles and the villages under the chase, broadly BH21, under Dorset Council. 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.
Questions
Cranborne questions we get asked
Is an external system realistic inside the conservation area?
It needs an application and it changes the appearance of the street, so in practice it is rarely the route here. We would look at a breathable lining inside instead.
Is foil backed insulated plasterboard safe on an old wall?
Often not. It seals the inside face, so moisture that used to leave into the room stays in the masonry. On a solid or rubble filled wall we would use wood fibre and lime.
What happens to the floor joists built into the wall?
They get colder once the wall is lined, so they are the detail we take most care over. We keep the joist ends ventilated rather than sealing them into the build up.
Could a lining bring on more condensation?
Not if the ventilation goes in with it. A tighter room with the same amount of moisture in it needs trickle vents and a working extract, and that is priced as part of the job.
What changes if the cottage is listed?
Yes, and on those the consent covers internal work as well as external. We will tell you at the visit what has to be applied for before anything starts.
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Get the wall looked at before you choose a system
Thomas comes out, works out what the wall is built of and prices the lining, the junctions and the ventilation in writing. The visit and the quote are free.