Wall insulation in Beacon Hill, and cavities that are already part filled
A third of the houses here were built with boards in the wall and a clear gap in front of them, and that gap is there for a reason.
The site visit is free and so is the written itemised quote. Thomas Hannen prices every job himself.
Roughly a third of the housing around Beacon Hill went up between 1983 and 2008, and houses of that age were often built with insulation already in the cavity. Boards or batts fixed against the inner leaf leave a clear gap in front of them on purpose. Blowing that gap full is not a top up, it is closing a drainage channel somebody designed in, and it is how a dry wall becomes a damp one.
So the calls here divide neatly. Owners of the newer houses who have been told their walls are uninsulated and are not sure that is right. And owners of the older half of the stock with a wall that runs cold, or a bedroom with mould in the corner.
Either way we open the wall and look. One small drilled hole and a borescope shows whether there is anything against the inner leaf, how wide the remaining gap is and whether it is clean and dry. The site visit and the written itemised quote are both free.
The work
Reading a cavity that may already have boards in it
Part filled, full filled and empty. Three different walls that look identical from the garden. An empty cavity can usually be filled. A full filled cavity, blown at some point in the past, needs checking rather than topping up. A part filled cavity, built with rigid boards against the inner leaf, was designed with a residual gap and generally should be left alone.
Why the gap is there. In a part filled wall the boards keep the heat in and the clear space in front of them lets any water that gets through the outer leaf run down and out at the base. Fill it and you have bridged the cavity along its whole height. That is the mechanism behind most of the damp that gets blamed on cavity insulation, and it is entirely avoidable.
Cavity fill where it does suit. On the older houses, where the borescope shows a clear, dry cavity of a usable width, the wall is drilled on a pattern, filled and made good in a day. Bonded polystyrene bead flows around the ties and stays put; blown mineral wool is the older method and it still performs in a clean sheltered cavity.
Internal wall insulation, IWI. For solid brick and block, or a cavity too narrow to fill, the lining goes inside: insulated plasterboard bonded to the masonry, or a batten and stud frame filled with mineral wool. PIR laminate such as Celotex or Kingspan reaches the target in the least depth, with the vapour control layer taped so warm air cannot get behind it, per BS 8000-8.
External wall insulation, EWI. Boards, a render carrier and a render finish over the elevation. It keeps the room size, warms the masonry through and deals with the joist ends. With nothing listed and no conservation area here, the appearance is genuinely your own decision, which is not true in most of the villages around this one.
Fill that has failed. Wool blown in decades ago settles and leaves a cold band under the eaves, showing inside as black mould along the top of a wall. A wet cavity where water bridges gives damp patches that come and go with the weather. Both begin with extraction, drilling and vacuuming the old material out.
Junctions, ventilation and draughts. Reveals, the threshold, the floor junction and the joist ends are where the heat loss concentrates, and a thermal bridge left at any of them gathers condensation whatever the u value beside it. Reveals take a thin board or aerogel. Then trickle vents, a working extract fan and clear air bricks, because airtightness without ventilation makes a warm house mouldy, and Approved Document F sets what is expected.
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.
Beacon Hill is under Dorset Council. There is no conservation area and nothing listed here at all, which is unusual on this patch, so external work is an ordinary permitted development question rather than a heritage one and Planning Portal guidance on external walls is the place to check it. Where an existing wall is upgraded, regulation 23 sets what the finished element has to reach under Part L.
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 1990s detached house with a part filled cavity, an older brick house on the lane and a bungalow on a sloping plot are three different jobs before a hole 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. We are about eight miles away on the Wareham road, so an address around Beacon Hill is normally looked at within a day or two. The phone is answered 24 hours for emergencies; scheduled work runs Monday to Friday, 8am to 6pm.
Worth knowing
A wall built with insulation in it is a different job
Part filled cavity construction became normal in this country during the 1980s and 1990s, and it is why a great many perfectly good modern walls should never be pumped. The builder fixed rigid boards to the inner leaf and deliberately kept a clear residual gap in front of them, usually around 50mm. That gap is not wasted space. It is the drainage route for anything that gets through the brickwork, and the cavity trays and weep holes at the base exist to let it out.
You cannot see any of that from outside, and a survey that judges a house by its age will get it wrong in both directions. So the check is the whole job here: drill once, look, and find out whether you are looking at boards and a gap, a clean empty cavity or something that was blown twenty years ago. If it turns out your walls are already part filled, the honest answer is that the wall is largely done and the money is better spent on the loft, the draughts and the ventilation. That answer costs us the job and it is still the right one.
Who you are dealing with
A local firm you can check
We cover Beacon Hill, Lytchett Minster, Organford and the Sturminster Marshall side, broadly BH16, 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
Beacon Hill questions we get asked
How do I know if my cavity is already part filled?
One drilled hole and a borescope. You can see the board against the inner leaf and measure the gap in front of it, which is the difference between a fillable wall and one to leave alone.
What happens if a part filled cavity gets pumped anyway?
You bridge the drainage gap from top to bottom, so water that used to run out at the base now reaches the inner leaf. That is the classic cause of damp blamed on cavity insulation.
My house is from the 1990s. Do I need anything doing to the walls?
Often not. If the boards are there and the gap is clear, the wall is largely done and your money goes further on the loft, the draughts and the ventilation.
How long does a cavity fill take where it is suitable?
A day for a normal house with clear access, drilled and filled from outside, with the holes made good in mortar matched to the wall.
Can I have insulated render here without permission?
There is no conservation area and nothing listed at Beacon Hill, so the appearance is your own choice. It is still worth checking the permitted development position for your own house.
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Find out whether your wall needs anything at all
Thomas comes out, borescopes the cavity, tells you straight if it is already done and prices anything that is worth doing. The visit and the quote are free.