The question is why have they rotted? (No damp proof course?) It's no longer the practice to build bits of timber into the wall for the joists to rest on. I would be tempted to remove the wood a bit at a time and put bricks in or similar that will fit if bricks are too big.
Something will have to be done about the DPC, maybe a chemically injected one. You can hire the equipment to do this.
You might well find the joist ends have rotted too much to be left. Even more likely if the wall are solid rather than cavity. If so, consider concrete floors rather then replacing the timber.
A lot also depends on the relative heights of the ground outside and the floor inside.
You need to carefully consider all the work, it might actually be better demolish the walls, even the entire building if the roof is bad too.
These jobs can grow like Topsy. As you get into them, more and more defects become apparent.
I had exactly this problem in my last house. Further to Phil L's reply, this was in internal half-brick (4 1/2") walls and the inner leaf of 9" external walls of an Edwardian semi in the Midlands. 4x2 or thereabouts had been layed on a bed of what looked like a black mortar, presumably intended as a dpc. Ground floor joists were layed on the wallplate, with brickwork infill, and the rest of the wall built up from there. Lengths of it had almost disappeared, as had many joist ends, and the dry rot showed every feature described in all the books. There was so much white furry fungus it looked like a dead polar bear under there.
Starting with lengths where there was absolutely no support from the wallplate, I chopped it out (mainly with my fingernails) together with whatever of the next couple of courses of brickwork fell out with it, and built short lengths of new brickwork on felt dpc (this was 35 years ago). Once the new mortar had cured, I moved on to the next section. The dry rot was so extensive I replaced the floor with concrete, otherwise I'd have used joist hangers. In one area, the dry rot hyphae, around the diameter of a biro, had spread right up the wall, under the plaster, till they merged with those from the rotten 9x9 timber lintel over the bay window.
The house is still standing, so the method must have worked. I think the main lesson was to do it in short sections. I didn't try to jack the wall because walls seem to settle irreversibly in that once a crack opens, mortar and brick dust fall in, then won't compress to allow it to be reversed.
There is a DPC, and the wall is the inner leaf of a cavity wall construction.
The cause of the rot is the Cavity Wall Insulation ( CWI ), glass wool made by a reputable company.
A few years back, the bedroom floor collapsed and I investigated. I found rotten wall plates, joists and floor boards. The CWI had soaked up the water from the bottom of the cavities, and even at two feet higher than the DPC, was just like a sponge full of water. I got the BBA (British Board of Agrement, the body responsible for the certification of building materials and techniques) out to inspect. The inspector stated that the insulation material was certified approved, and the installation was performed correctly, and that what I had showed him could not have happened.
So i removed every third brick from the outside wall just above the DPC, vacuumed out the CWI below this level and installed cavity brush horizontally around the (detached) property, and installed extra air bricks in both leaves, sometimes offset by one brick to prevent wind noise.
Ours is the only property round here with suspended floors, all the others are solid. The property was built in 1953/4, and there is a 100m clay bed beneath the area leading to very poor drainage.
I have used bricks in the past as a temporary replacement before in other parts of the property to 'prop' up the walls, but in this case, I think the wall has dropped a bit.
I'm not sure what you mean by "half-brick" walls. Our inner walls are brick and mortar to the DPC, which I believe was a liquid poured onto the mortar, then another bed of mortar, then timber, then mortar again with brick infill, then big grey blocks that are similer to 'breeze blocks' for the rest of the inner wall.
I do not have any dry rot, thankfully, but there is white furry fungus nearly everywhere in the voids under the floor on, dead organic matter, not the property construction materials.
I'm pleased that you had success with your problem.
The convention is that walls built of stretchers, i.e. 4 1/2 inches thick, = are referred to as half brick. Discounting walls built with bricks on edge = this is the thinnest you can do with regular bricks, and is the thickness o= f most of the individual leaves of cavity walls. Before the introduction of cavity walls it would be normal for the external= walls to be 1 brick (9 inches) minimum, with the walls of larger houses of= ten 1 1/2 or 2 brick thick at lower levels.
referred to as half brick. Discounting walls built with bricks on edge this is the thinnest you can do with regular bricks, and is the thickness of most of the individual leaves of cavity walls.
walls to be 1 brick (9 inches) minimum, with the walls of larger houses often 1
1/2 or 2 brick thick at lower levels.
on myhouse the garden had built up higher, covbering the airbricks which then let in water.
I have dug a moat around the house, and hope that future generations wont fill it in with earth and repeat the sorry saga! [george]
I know that it isn't coming from the roof, nor from leaking gutters, but it was from the CWI 'sucking' up the water from the bottom of the cavities, before the CWI was removed. The cavities fill with rain water after prolonged rain. Wetness can also be seen on the surface of the solid sub-floor (?) after heavy rain if the floor boards are lifted.
It could also be penetrating damp though, bricks are not waterproof ...
I am having the South and West elevations re-pointed in a couple of weeks as they have deteriorated badly, though the current wall plate concern is on the other corner (NE) of the property.
as well as digging a moat around my house, and installing french drains, i left some pits so i can look at the water level at various times, after rain, after drought, and see where the local water table is at.
Maybe Ill' put some plastic french drain vertically in these holes with a cover over it so i can check this over the years when i've tidied up the outside of the house. [george]
This isn't possible I'm afraid, and whoever has told you such garbage has been lying. CWI is waterproof - completely 100% waterproof, it's tested and tested again and cannot 'wick' moisture upwards, unless you got someone to fill the cavities with shredded newspaper? - I'm sure I read earlier that they were done with blown glass fibre?
I'm afraid you've done more damage than good by removing part of the CWI - walls need to be 100% filled to be effective not just against heat loss but water penetration too
Yes above is correct. The fibres they blow in are treated to make them water repellent (slicon I think) I think you're back to interstitial condensation. Warm moist air condensing out in the insulation. The problem is once the water is in the insulation it remains there and may have caused/made worse your rot problem. The only way to dry it out is by removal. Wet insulation is pretty ineffective anyway.
If you have water under the floors, you've got to get rid of it. Either by a drain or with a sump and a pump. Best to stop it from getting in if at all possible.
Imagine removing a brick / block from the internal wall two feet above the internal floor, and finding the CWI soaking wet. It was literally like a sponge. Squeezing it released lots of water. Are you (Harry) saying that interstitial condensation can penetrate the wall to that effect ? What about penetrating damp from the outside ? I would have thought that more likely.
I do not understand how if the CWI is treated to repell moisture, that it can collect and retain moisture to the extent it has.
So possibly, I need to remove the CWI and somehow put a vapour barrier on the walls that have outside components.
The area is situated on a clay bed of 100m depth, there is poor drainage and the cavities are somewhat lower than the ground level, therefore they are a collection point for the rain. Should I approach the Water Authority about connecting to the sewer, or storm drains in the road ? Then I might get subsidence as the clay dries out and shrinks. I suppose then I need to get the place underpinned.
Phil, with regard to me making the problem worse by removing the CWI, now the timbers do not have wet material touching them and also there is now more ventilation to dry the sub floor voids, this would have been better had I not ? I cannot agree with that. The timbers are now dry and rotten (and have shrunk), whereas before they were wet and rotting. Would it have been better to leave them wet ?
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