Rotten Suspended Floors & Improving Sub-Floor Ventilation

[njwilson]

Sorry for the delay in responding - work forever gets in the way of all this... fun... stuff.

I've finally removed all of the timber from the floor, and I've found the source of the problem... which is that the air bricks don't actually go anywhere!

The front wall is three bricks thick at the foot of the small bay window, and on the outside there is one air brick in either corner of the bay. However, on the inside there's no correlating hole. There's a gap in the bricks in the middle of the bay that's two bricks deep, and this just dead-ends against the outer wall. The sleeper wall nearest the bay also has a venting gap in the middle, but none of the others have.



It makes no sense. I even had a rummage around, to see if there was an early rudimentary cavity wall that the air bricks channeled into for some reason... but nothing. The sub-floor has never ever had ventilation, except for when it collapses every 50 or so years.

Also, it seems the dry rot was confined to the corner to the right of the chimney breast and every other part of the room had been chomped on by beetles.

Also also, there was no DPC under the wall plates in the middle of the room - they were laid directly onto the masonry. What looked like engineering bricks were just very filthy red bricks. The concrete hearth was plonked directly onto the wall plates too, so this needs removing.

 

[bobasd]

if you posted the photos i asked for you might be helped a bit more?and photos of the hearths.
ddry rot climbs up behind plaster and sometimes up flues or through brickwork.
is the outside ground level very high?
as advised by others above, you need to honeycomb all partition walls and knee walls.
9"x9" plastic air bricks give good ventilation.

 

[njwilson]

Room:

Hearth area:

Window Area:

 

[njwilson]

The ground outside isn't too high. At the front there's a rudimentary French drain along the front wall and to the rear the concrete in the side return slopes away from the house.

There didn't seem to be any sign of dry rot or beetle activity above the level of the floorboards - the skirting boards were all unscathed, even the few remaining scraps of original Victorian ones.

 

[bobasd]

insulate and clip all copper pipes,level out sags, before covering up.
remove all debris waood as you work to give a clean space.all wood bits must be removed.
replace kneewall plates over strips of DPC.
knock a few honeycomb holes in knee walls.
move the hearth slabs and dig out soil and debris inside the fender wall to 450mm.what are you going to do with the c/breasts and hearths?
open up and sweep and then vent chimney breast flues. do upstairs c/breast flues as well.
first fix any new elec or comms and anything else while floor is open..
photos of french drain. and concrete side return whats that ?

 

[njwilson]

Already got lagging to go on the pipes, and the debris wood is already swept away.

Not sure how much 'give' the pipes have for bending them straighter - they seem to have been installed wonkily to start with, if some parts are anything to go by. Don't want to inadvertently add damp back into the room by mucking about with them too much!

The old chimney does need venting - not sure yet what to do with it. In an ideal world, a small solid fuel stove would be great. But with budgetary constraints, I may have to make do with either putting a small vent in there, or excavating the builders' opening and use it as a niche. With that in mind, I'll probably remove the concrete hearth and floorboard right up to the chimney breast. The upstairs and dining room fireplaces are still present, so they're fine.

The side return is the small, dark and invariably damp bit of the garden in Victorian terraces that the dining room backs on to and runs alongside the kitchen exterior wall. Mine is concreted, but done so it slopes towards a drain on the property boundary. Will supply photos of the French drain when I have chance - but it's just a small trough below the air bricks, with the rest of the front garden concreted (again, angled away from the house). It could do with being weeded, excavated and refilled with gravel over a weed barrier, though.

Have you ever run into a house with air bricks that lead to nowhere, though, as mine seem to? It's very odd.

 

[bobasd]

no one cuts a french drain unless theres a problem with damp.
lots of times brickies used to fake doing a proper job and didt vent proply.
sometimes telescope air bricks/vents are needed if ground level is too high.
do you now where your DPC is?
whats happening in the dining room? you need to honeycomb the dividing wall from living room and all other dividing walls.
all flues need sweeping in old houses

 

[njwilson]

It looks like the French drain comes from when the concrete was poured, rather than being cut in afterwards. In any case, I'll be getting rid of all the concrete in the front and back gardens at some point.

The house has no DPC - it was built before they were mandatory, and none has been retrofitted. There's a lot of the original plaster left in the house so it looks like it's done okay without it, even with an unvented floor. Poor gutter maintenance and condensation seem to be the main culprits for the few areas of plaster deterioration/staining above the floorboard level. The bricks under the floor don't seem obviously damp, except where they were piled up with sodden loose soil and old rotten wood (8 big rubble sacks of it).

I've no idea what state the subfloor of the dining room is yet - it's piled with all the furniture from the living room. I'll have to tackle one room at a time, which isn't ideal, admittedly.

The joists in the hallway, I noticed, were set in pockets in the walls, and on the shared wall with the living room the pockets punch right through and are a fair-sized gap (about half a brick wide). Would that be enough ventilation between those two rooms? I don't know enough (or anything) about structural engineering to know if it's fine to knock out more bricks from the wall if it's already half a brick short every 40cm.

 

[Nige F]

Have you ever run into a house with air bricks that lead to nowhere, though, as mine seem to? It's very odd.

Yes, my last bungalow - 1920's- was like that. As to the wonky pipes, remember they had to be threaded under the floor through traps. As long as the dips rise up to vent ( through a rad, even in another room ) they'll be fine.

 

[njwilson]

I've knocked out a few bricks from the sleeper walls to aid ventilation, and it turns out that there was a DPC... or an attempt at one.

There were engineering bricks, but not laid in a single, continuous course - just dotted about at random. And then there were some layers of a bituminous substance used as a mortar, but again not forming a continuous layer - just blobbed between some of the bricks at random intervals. The wall between living room and dining room does have a layer of bitumen right along the base of it, but not the other three walls.

 

[njwilson]

Okay, everything's been given a thorough scrape-out and sweep down. A few unearthed revelations...

The hole in the middle of the bay leads to a perforated brick that butts up against the soil outside, and the hole is actually a slate-lined channel. What would be the function of actively letting ground water into the subfloor, as this must?

Also, there are holes for the air-bricks... they're just much higher up the wall than I thought they would be and are mostly covered by the skirting board. The street is on a slight slope, with my house near the top, and with subsequent houses in the terrace getting larger steps to their front door as the ground falls away. I assume, rather than dig out the ground, they just crammed the air bricks in.

Would chiseling a slope into the lower bricks to create more of a hole below the floor be useful?

Also, I noticed that the foundation of the building seems to be engineering brick, and on top of this is a layer of slate - but it's all very much underneath ground level, and always would have been. Seems pointless, even more so with a perforated brick channelling water over these layers.

 

[bobasd]

like i asked you before. how high is your ground level? why not post photos of the outside at ground level, front and back?
the knee wall nearest the bay is a later remedial measure.its not original.
why not knock it down and set your DPCwrapped joist tails in pockets cut in the brickwork like it would have been originaly.
you could also knock dpwn both middle knee walls and rebuild one true honeycombed knee wall in the ceentre of the span.

any high air bricks that come out completely behind the skirting are useless, they can be removed, the brick below chisled down and
like i said before you have options of larger air bricks or telescope air vents both front and back.


the right hand alcove skirting needs removing and you having a look for fungus strands.

in the outside walls,its possible the slate and bitumenDpc is working so dont mess with it.maybe its bridged by high outside ground levels?
how were the alcove joists supported wwhere they hit the chimney breast?cant tell from the photos

 

[njwilson]

The ground level outside, front and back, is about 1-2" below the air bricks. The houses either side have a similar gap, so it seems that's how it's always been. At the moment, the view of the air bricks is obstructed by debris from the renovation, but I'll take a photograph when it's cleared over the weekend.

I think the sleeper wall nearest the bay is original - it's made of the same bodge of random engineering bricks and bitumen as the others. There's no indication that the joists were ever in pockets, except in the hallway. With regards honeycombing them properly, I've never actually done any bricklaying before and whilst I know they don't have to look pretty... I'd still rather not start mucking about too much with the structure of the building on my own. Currently, I've knocked out holes in the centres of the sleepers that are one brick wide and two bricks tall - a little larger than the hole in the sleeper nearest the bay.

The air bricks aren't completely covered by the skirting - it's about 50% in/out. At the moment, although it would be ideal, taking them lower or installing double-height ones would mean cutting out the concrete in the front garden. It's why I wondered about cutting a slope in the (internal) brick below, so when I've time/money to excavate the front garden a little I can fit in some larger air bricks.

The slate and bitumen is very much below ground level - they're right above the foundation where the bricks are arranged in wide tiers. It's possible there's another layer of slate buried in the mortar higher up, as the one I've found so far wasn't very obvious.

The joists in the alcoves are/were supported by a mini sleeper wall 1 brick wide built up against the breast.

 

[bobasd]

fair enough, im wrong about that wall. thing is that three sleeper walls and a dividing wall will cut down on ventilation.
knee walls arent structural and brickwork can take lots of cut pockets.
true honeycomb gaps are often only half a brick openings staggered in each course of brick.
clean out the air holes in the air bricks and all the muck built up on the slate .
get a roll of 100mm x 30/50M DPC and lay it under all plates or joists on brickwork.

 

[njwilson]

Already got the DPC bought.

After about 12 hours of heavy rain, the living room is now a collection of very modest ponds (about 1-2cm deep) - no sign of it pouring in, or it being the product of a leak, but rather just seeping up where the ground is lowest. I guess a high water table would explain the squelchiness of the ground when the boards were first lifted.

I assume that adequate ventilation will be fine for dealing with this, and that putting a DPC on the soil itself, as has been suggested elsewhere, would just create permanent ponds?