Wall insulation in Holton Heath, and cavities too narrow to fill
An older cavity can be barely 40mm clear and half full of mortar droppings, which is the one wall nobody should blow full.
The site visit is free and so is the written itemised quote. Thomas Hannen prices every job himself.
Not every cavity is wide enough to fill. The inter-war houses around Holton Heath were often built with a narrow gap, sometimes barely 40mm, and plenty of those cavities are part full of mortar droppings that fell in as the wall went up. A narrow, dirty cavity is the one wall nobody should blow full, and it is the one a surveyor working from the pavement will happily quote for.
The calls that follow are predictable. A wall that has gone damp on the inside face after a fill. A room that is cold along one side whatever the heating does. Or an owner who has been quoted for cavity insulation and wants a second opinion before anybody drills.
We measure the gap before anything else. One small hole, a borescope, and you can see the actual width and whether the ties are loaded with mortar. That is a five minute answer to a question that decides the whole job. The site visit and the written itemised quote are both free.
The work
Measuring the gap before anything is blown into it
How wide is wide enough. A cavity needs a genuine, clear gap for fill to work, and the useful number is what is actually clear rather than what the wall was drawn as. Snots on the ties, a leaning inner leaf and mortar sitting at the base all eat into it. Where the clear gap is too small we say so, because a partial fill is worse than none: it bridges in patches and leaves cold patches between.
A cavity full of rubble. Older walls collect mortar droppings at the base and on every tie. Blow bead or wool into that and the material packs against the debris, water crosses at each bridge, and what you get inside is damp patches that appear after driven rain. This is the failure mode we see most often on the older houses out this way.
Where the wall does suit fill. Plenty here do, particularly the 1980s stock. Clear, dry and wide enough means drilled on a pattern, filled and made good in a day. Bonded polystyrene bead flows around ties and stays put; blown mineral wool is the older method and it still works in a clean, sheltered cavity.
Internal wall insulation, IWI, when the cavity is out. Insulated plasterboard bonded to the masonry, or a batten and stud frame filled with mineral wool and boarded over. 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 the board, per BS 8000-8. On older brick and block a breathable build up keeps the wall able to dry.
External wall insulation, EWI. Boards, a render carrier and a render finish. It is the strongest option on a narrow cavity house, because it does not care what the gap is doing: it warms the whole wall from outside and puts a weather coat over the brickwork. It keeps the room size and it changes the look of the house.
Fill that has failed. Slumped wool leaves a cold band under the eaves and black mould inside along that line. A wet cavity gives penetrating damp on the weather side. Both start with extraction, drilling out and vacuuming the old material, and on a narrow wall the refill is often not the right answer at all.
Junctions, ventilation and draughts. Reveals, the threshold, the floor junction and the joist ends carry the heat loss, and a thermal bridge left at any of them collects 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 turns a warm house damp, 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.
Holton Heath is under Dorset Council. There is no conservation area over the settlement and five listed entries in the area, so for most addresses this is a building control question rather than a planning one; Planning Portal guidance on external walls covers where an external system does need permission. 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. An inter-war semi with a narrow cavity, an 1980s detached house on one of the closes and a bungalow set back off the main road 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 under nine miles away on the Wareham road, so an address at Holton Heath 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
Why an inter-war cavity often cannot be filled
When cavity construction first became normal between the wars, the gap was there to keep water out, not to hold anything. Builders left the smallest space that would do the job and used butterfly ties that catch mortar as easily as they hold the leaves together. Nobody cleaned the cavity as the wall went up, because there was no reason to. Ninety years later the result is a narrow gap with a ridge of hardened mortar along every tie and a heap of it sitting on the base.
That is the wall to be careful with. Blown full, it does not insulate evenly, and every lump of debris becomes a bridge that carries driven rain to the inner leaf. The damp that follows is blamed on the insulation, but the real fault was filling a wall that was never suitable. So the measurement matters more than the material here, and where the gap is too narrow or too dirty the honest answer is an internal lining or an external system instead. It costs more and it works, which is a better trade than something cheap that causes a problem.
Who you are dealing with
A local firm you can check
We cover Holton Heath, Sandford, Organford and the Wareham St Martin 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
Holton Heath questions we get asked
How narrow is too narrow to fill?
It is the clear gap that counts, not the nominal one. Where debris and snots have eaten most of it there is nowhere for the material to sit evenly, and we would advise against filling.
Can the mortar be cleaned out of an old cavity?
Not in any practical way on a standing wall. That is why the measurement decides the route, and why an internal or external system is often the right answer on these houses.
Somebody has quoted me for a fill without drilling. Should I be worried?
Yes. Nobody can see the clear width or the debris from outside, so that quote is a guess. Ask for a borescope check before you agree to anything.
How disruptive is lining a room compared with a fill?
Considerably. How long it runs is several days once the room is cleared, the boards fixed, the joints taped and the plaster made good, against a single day for a fill.
Will external render work on a narrow cavity house?
It is often the best option, because it does not depend on the gap at all. It warms the whole wall from outside and keeps driving rain off the brickwork.
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Get the gap measured before anybody drills the wall
Thomas comes out, reads the cavity with a borescope, says honestly whether it will take fill and prices the alternatives in writing. The visit and the quote are free.