Venting A Subfloor

[Iggifer]

I have a 1920's terrace which has a wet rot problem in the suspended timber floor in the lounge. The kitchen (to the rear of the lounge) is a concrete floors and have just fitted a new kitchen and kitchen floor (d'oh!).

Wet rot is at it's worst on either end of the timber joists (obviously) but the back of the floor has mould growing under the floor - front is just wet. The subfloor is just exposed clay (once I've cleaned 100 years of debris out anyway)

I've got 50% of the floor up and both front facing air bricks are clear, but the two salt glazed pipes that run from the dividing wall to the rear of the house for exhaust (or intake I guess depending on the wind direction!) are both blocked. One appears to have collapsed and the other, has been butchered by the water company - new MDPE main has been brought in at some point in the past and to make life easy they've gone straight down the duct and come up in the kitchen floor nowhere near the air brick - so have presumably destroyed the duct in the process.

As I see it I have a few options:

1. Replace with tanalised timber & celotex and worry about it when the kitchen gets redone.
2. Mechanical ventilation
3. Hardcore, concrete, celotex and screed the floor.
4. Block and beam.

If there are other options then I am open to suggestions. I suspect 3 & 4 are the most expensive options and 2 would require fitting the ventilation somewhere accessible. Option 1 is clearly the cheapest but I like to do things properly where possible

Rough drawing for visual representation attached.

Thanks guys

 

[bobasd]

pics of the lounge floor/joists and openings for rear vent pipes would help?
so would pics of the rear & front elevations?
9" x 6" plastic air bricks are best.

you've presumably fitted new units and a new kitchen floor covering? what does "when the kitchen gets redone" mean?
doubtful that the water company did any interior work in a residence?
where it enters the property, the MDPE might now be vulnerable to freezing?
have you tested both the external and the internal isolators for opening and closing freely?
do you have a water meter (where is JohnD the water meter man when we need you?)?

are all FFL's in your property higher that the external ground level?

sketched diagrams need to be fully annotated for the reader to understand.

 

[Iggifer]

What photos I have on my phone attached - don't have many of the joists.

Yes new kitchen units and fully tiled floor. "When the kitchen gets redone" means literally that, when I get sick of it in x years time and rip it out, will give me the opportunity to repair the original salt glazed ducts - obviously had I realised the floor was so bad I would have done that first.

No, probably wasn't the water company, but the outcome is the same. The MDPE is under a concrete slab out the front, and before I do any work with the floor I'll lag what I can inside - particularly as once I insulate the floor I suspect the average temperature in the void will drop somewhat.

Yes, FFLs are all above outside ground level, front by about half a brick course, and then the back is a course and a half/two courses.

No water meter, internal isolation works fine, I haven't checked the external one (have had no need to do so as yet) but I will do.

Re: the diagram, the red is air bricks/salt glaze duct (route is unlikely to be accurate as they curve). Black is the PILC electric main, yellow is the new-ish gas main and blue the MDPE water main.

Front Elevation

Rear Elevation

Joists

Air channel from front air brick (totally clear)

 

[Iggifer]

For some reason the forum wouldn't let me upload an image after the first one so apologies for the giant images. Wouldn't even let me add them to my albums separately

 

[bobasd]

thanks for the images - but a little info with each pic helps the viewer orient himself etc.

the front & rear air bricks appear to be too high to be useful - do they somehow vent the sub-area or do they simply vent the upper rooms above the FFL's?
the rear airbricks cannot, as far as i can make out, be venting through the salt glaze pipes you mentioned?
the cause of your damp difficulties is condensation due i'd say from a lack of through ventilation.
you are right and lucky that its wet rot affecting your joists - not dry rot.
there have been historic repairs to the joisting.
perhaps it would be wise to replace the whole of the lounge floor and any timber plates and skirting.
all joist tails etc. must rest on DPC material.
the white dotted stuff is the effects of condensation - no big deal.

all the wood debris should be removed from the subarea - same with any timber fixing plugs in walls.
there's two courses of blue engineering bricks which presumably act as a DPC - there's also evidence of chemical DPC injection holes fwiw.
the hearth will need digging out and damp proofing - see other posts ref doing this. pics of the chimney breast and hearth would help?
its possible that all plaster to a certain height will need knocking off and rendering with sand and lime.

you have a rainwater down pipe at the front - where does that RWP discharge to?
at the rear there is a gulley - is that gulley clear and discharging to a manhole?

 

[Iggifer]

Thanks Bob (?)

All photos of the joists are to the front of the house, and the one under the boards is also the front.

The air vents in the front wall are connected by missing bricks to the last photo, just an opening in the wall that makes it's way up to the air brick (no cavity obviously) I'm assuming it's just working like a telescopic air brick but without this new fangled plastic. There are no vents in the front room certainly, but now I've looked back through photos, the smaller air brick on the left of the back door is a room vent.

Some poor quality (used to be a council house) repairs, yes. They've just bolted new timbers to rotting/rotten ones without taking the entire span from wall to wall.

I think replacing the floor in it's entirety is a given at this stage, I've ripped up about 1/2 the boards so far and there's been very little worth salvaging - skirting, archi, plaster etc is either all gone or going too so that's no issue. Good note about sand & lime though, thanks.

Will get some pics of the chimney breast/hearth next time I'm over there, it was a bad concrete hearth that basically fell apart as I removed the timber around it and now it's a brick rectangle frame filled with mud, broken bricks and whatever else the original builders filled it with.

Those white dots are actually water droplets reflecting the camera flash, that's how wet it was.

I've already started work on clearing out all of the debris, not just wood. About 25 gorilla tubs so far. I figure the less stuff that's down there that has the ability to hold water, the better.

Not sure where the RWP discharges to, I will have to take a look. The gulley at the back is clear yes, as to whether it flows to a manhole, I'm not sure, according to the Severn Trent search the nearest manhole is 4 houses away. There is a rodding point in that awful concrete patio (can just about see it next to the gulley)

Good eye on the chemical DPC too btw, I know it's there, and I had to zoom in to see it

Thanks