Back in the year dot when we bought our first house one of the financially crippling conditions of the mortgage was replacement damp course and woodworms treatment. (Another being the fact that as we exceeded what we could get on multiples they charged an extra 0.5%, to people who were already stretched, but that's another matter!).
So my daughter in a 60s ex-council house in Birmingham has a problem with damp. Some is obvious and is condensation but the other is more noticed by just a bit of mould round the skirting I think.
She had in two specialist companies for quotes. Both came up with similar conclusions proposals plus one gave her some good advice in the quote about how to address condensation. They both were going to strip back plaster and inject. Also both recommended a PIV to be installed.
That all sounded quite plausible to me, except I had to look up what a PIV was and what it did.
However she delved into damp courses and has proven to herself, but also to my surprise and near-satisfaction me, that damp courses don't often break (unless breached by e.g. soil above it) and the industry built around it, and the solutions, which has been in existence for many years, is all a bit of a com, unless you live in a middle ages house.
So in the short term she is going to get a PIV (as they house is prone to condensation) and address the issues which lead to condensation as best she can but not get the damp course work done until she sees how that pans out. "Saving" her about £2k.
I'm sure there are opinions here but here is one of the articles which throw some doubt on the whole business. alpinesurveys.co.uk/damp-proof-course/
This describes PIVs well, and I think I might get one, for the fresh air and dust management rather than any damp problem www.permagard.co.uk/advice/positive-input-ventilation-the-pros-and-cons
Last edited by: smokie on Sat 30 May 26 at 13:44
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Our daughter had a similar damp end gable at ground level on the survey when buying her house three years ago. My suspicion was that it was condensation due to the house having been unoccupied for a few months before she moved in. She also had condensation in the loft which had a newish tile roof with felting. One upstairs bedroom also had a bit of mildew on the ceiling. I wondered if these two issues were due to poor loft ventilation as there no venting tiles. The loft hatch also was badly fitted.
In the event she ignored my suspicions about the gable end and had a chemical DPC installed by a local firm. They did a tidy job and the damp has gone but whether it’s because of the work or simply because the house is now occupied, who can say. The loft and ceiling issues have been resolved with vented tiles and a PIV installed on the landing. I am not sure how much they spent on all this but it wasn’t very expensive. And they’re happy.
As for the PIV it’s whisper quiet but I don’t understand how it works. Outside air that it draws from the loft must surely be higher humidity than the indoor air most of the time. So they are drawing in damper, not drier, air. And the idea that this low powered fan can meaningfully pressurise the house seems a stretch.
Having said that it appears to work.
I’ll be interested if anyone on here can shed any light on the science here.
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I had a problem with a newly laid laminate floor in my 1960 built bungalow. 1965 building regs required a damp proof membrane to be laid and concrete flooring poured on top. Testing showed my concrete slab to have 90% humidity!
I've since heard of other pre '65 built houses also having damp/condensation problems
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Before spending money on expensive systems try simple ventilation. Window need to be opened especially when cooking showering or running baths. Bedrooms need ventilation at night. The human body loses a litre of water while you sleeping. The other side of the equation is that the fabric of the house needs to be kept warm to avoid condensation on surfaces.
Unfortunately the understandable tendency to shut all windows and stop all draughts to lower heating bills has led to damp problems in many homes
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You can't beat modern (well-built!) homes. I've lived in 22 properties since 1952 and have experienced everything from bed bugs, ice on the inside of windows, rising damp, wood worm, and yes, black mould, which was quite bad in a 1950s bung due to cavity wall insulation and no trickle vents.
A previous owse to our present one was a highly insulated timber-framed new build. Our present property is conventional block-cavity-block. I couldn't produce mould in either property even if I tried.
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>> and yes, black mould, which was quite bad in a 1950s bung due to cavity
>> wall insulation and no trickle vents.
Why do you think cavity wall insulation would cause mould? I had it installed in one house resulting in less heat loss. It certainly made the place warmer. Wouldn't a warmer house result in less condensation?
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>> Why do you think cavity wall insulation would cause mould? I had it installed in
>> one house resulting in less heat loss. It certainly made the place warmer. Wouldn't a
>> warmer house result in less condensation?
We had problems with condensation on the walls of our previous house, particularly in corners and behind furniture after replacing I'll fitting and draughty softwood windows with UPVC. Cavity wall insulation would surely have raised the surface temperature of the inside walls and reduced the propensity to condensation.
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>>Why do you think cavity wall insulation would cause mould?
The cavity wall insulation caused bridging, which can occur when debris, mortar, or water crosses the cavity gap, especially in west-facing walls in areas where it rains every day and twice on Sundays :) compromising the barrier between the inner and outer masonry leaves. This bridging often centers on wall ties, which can act as thermal bridges or moisture pathways- if not installed correctly. The property didn't have trickle vents either which adds to the problem.
I removed some fitted bedroom and kitchen units and you wouldn't believe the black mould behind them.
The building was sick - didn't stay there long thank gawd.
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>> The cavity wall insulation caused bridging, which can occur when debris, mortar, or water crosses
>> the cavity gap, especially in west-facing walls in areas where it rains every day and
>> twice on Sundays :) compromising the barrier between the inner and outer masonry leaves.
Wall ties can and do bridge cavities without insulation being in the mix.
Mortar left on them during construction was a significant issue in seventies built houses; survey flagged it as a risk in more than one place we looked at buying.
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FIL (chippy) refused to consider cavity wall insulation, as he said it prevented water running down the cavity. I asked him where that water was coming from, he couldn't answer. He wasn't very academic or technical.
I know the properties I've had with cavity wall insulation were 'warm' and the one I had it installed made it much more comfortable.
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Jeff Howell, the guy referred to in Smokie’s first attachment, used to write regularly in DT about cavity insulation. As I recall the main issues were around poor installation in unsuitable properties in unsuitable environments. There are climate maps which can help determine whether the area is suitable. Basically don’t install it in exposed, high driven rainfall areas as the outer leaf is designed to cope with damp and condensation on its inner face. Cavity wall insulation can stop this breathability and lead to cold damp patches.
I don’t think the cavity is expected to cope with running water as that would ultimately pond on top of the DPC. Having said that weepers are often found in houses as part of window lintels and, if window condensation is any guide, I suppose some dripping inside the outer leaf is possible.
Intuitively it seems sensible to me that cavities need to have a degree of ventilation just as rooms do.
Also after market insulation pumped in by an oik with a van is liable to be hit and miss compared to a proper design and installation.
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” I don’t think the cavity is expected to cope with running water as that would ultimately pond on top of the DPC”
There’s slots in the mortar just above the dpc to let water run through the outer wall.
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Thanks, I’ve never spotted these DPC slots. I am sure none of my houses has had them. It makes sense though and I bet I start seeing them now. I must get out more though ;-)
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Water penetrates the outer wall, as bricks aren’t waterproof.
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As you may know I’ve been running my own Building business for many years (Est: 1977). I have fitted many positive pressure fans and have one in my own cottage for the last 15 years. Indeed they do work and work well. I also have one in my daughter’s property (who dries clothes on radiators) and she’s still under threat of bodily harm for that heinous crime! Again it works well. Nothing more to add really.
Both installed in the loft as opposed to and outside wall.
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Ahm thanks MD> Daughter has decided to go with one (along with changes in how they air the house and store stuff) to see what impact that has, before revisiting the damp course quotes. If i works for her I may get one too, not really sure why as we don't have a damp problem but it seems a Good Thing :-)
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Have a look at Peter Ward on Youtube he has some interesting ideas on damp. He tends to refer to the damp companies as 'damp wallys'.
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If you call a company that fixes damp courses, this is the likely solution that will emerge. Can be expensive and disruptive - it is worth checking other cheaper solutions first.
Houses with people produce a lot of moisture from cooking, bathing and even breathing. It needs to go somewhere - sometimes obvious, sometimes hidden in cavities and roof spaces where it meets a cold surface. Ventilation, particularly kitchens and bathrooms is cheap and easy to fix.
Other sources of damp can include failed mastic around window frames, gutters and downpipes leaking, blocked airbricks which should ventilate cavities, roof tiles cracked or missing, etc.
The other risk is related to well intentioned house improvements which were not part of the original design spec - eg: sealed UPVC windows replacing the "natural" ventilation provided by wood, extensions covering air bricks, bio-ethanol fires, cavity wall insulation creating a cold bridge.
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I have a relatively modern 90s property. There are no plastic weep vents to drain water off the DPC. I'm pretty sure there are 2 DPCs. One on the inner wall and one on the outer wall. Any water should soak into the footings.
There does not appear to be any cavity trays above downstairs windows either which should have weep vents to allow water to exit from the tray.
If you ever see these property 'snaggers' at work they often pull out weep vents which have been cut down and just pushed into the mortar to look the part.
I'm sure new builds have a bigger cavity with an air gap left between the cavity insulation and the outer wall. Presumably to allow to stop any penetrating water bridging into the insulation.
Last edited by: Fullchat on Sun 31 May 26 at 22:18
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Coincidentally I looked out this morning and next door had scaffolding up and guys taking off roof tiles. Talking to the workers it seems the roof had been spray foamed in the past and roof timbers (maybe just battens?) are rotting. Main trusses may be sound but either way it’s every tile coming off so it’s a big job.
They are opting for new tiles as the old ones were about 35 years old.
Needless to say the spray insulation cowboys are long gone.
The builders say they get half a dozen local roof renovation jobs each year as such houses go up for sale and can’t be mortgaged.
Thankfully our roof was never done.
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And known properties with spray foam can’t be let either (if you follow legit channels).
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>> They are opting for new tiles as the old ones were about 35 years old.
I had to have a roof done when the battens rotted, due to low slope angle and insufficient tile overlap in a '65 Wimpy built semi, the roofing company said. Original concrete tiles were re-used, with a number of new to add another row to increase the overlap. We weren't the first and several neighbouring houses have been done. Only one had all new tiles, suspected by a cowboy company
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Concrete roof tiles have a lifespan of 40 to 60 years. Not unreasonable to replace them if the entire roof being replaced after 35 years.especially if they not of tye best quality. Most of the cost of the job would be labour.
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>> Concrete roof tiles have a lifespan of 40 to 60 years. Not unreasonable to replace
>> them if the entire roof being replaced after 35 years.especially if they not of tye
>> best quality. Most of the cost of the job would be labour.
Most of the cost of my job was scaffolding!
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In my mind scaffolding is generally good value for what it allows one to do. £25.00 per linear metre x number of lifts.
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Damp course repalcement (and PIVs) - martin aston
