Floorboards are up - how do I tackle this?

Gizzydash · 5 Jun 2021

Hi Everyone,

Doing some renovations and curiosity got the better of me to examine what the state of the sub floor was like in one of the rooms before going on to decorate etc - suspended timber floor (1965 bungalow), roughly 3x3m - pictures attached.
There's one air brick, non-honeycombed sleeper wall in middle and wall separating next room has 2 holes punched at either end to let (I assume a small amount) air pass through.
Couple of things stuck out to me - complete novice:
Joists all moveable, pretty sure if I knocked a couple with little force they would fall over and couple not even attached (just suspended there).
Maybe it was just the day working but felt a lot more humid once I lifted the floor up.
I have a small moisture meter and ran it around various areas - most joists / wall plates coming up 10-15%. However wall plate furthest away from air vent was up at 40% and flashing off the scale in some places (wasn't crumbling or anything to the touch). Joists themselves are ~110mm.
I'm no expert in all this but seems the best course of action is to redo it all (new wall plates/joists) and probably add an additional air brick at the side (close to where high humidity readings were). I had thought about insulating but i'm not convinced, maybe just redo all the sub-floor, put a vapour control layer down and put floorboards back down.
Does this sound like the right approach - anything else I should be considering?

Thanks in advance

jacko555 · 5 Jun 2021

Not a builder but looks good for nearly 51 years, no rot or worm, and, fine without a vapour barrier.

Surely adding the floor back will tighten the suspended floor together.

Why bother redoing it all if there's nothing amis?

Or am I missing something?

I probably would suspended some insulation down there while the floor is up.

Gizzydash · 5 Jun 2021

Take your point about things not looking too bad for 50+ years

I suppose there are 2 main concerns - first being the relative instability in the joists but as you say maybe the floor tightens up that whole structure. Never having examined a floor like that before I expected to be able to stand on the joists to move around the room once the floor was up but that's a definite no-no, joists would easily fall over.
Second being ventilation and moisture - meter reading over 40% on the wall plate bit concerning long term and bit of a musty smell in the room which would indicate ventilation is not great. I know there's an air brick there on the opposite side of the room but feels like not enough air is getting pushed around the whole void - hence the high readings opposite too where the air brick is and air only able to pass over the gap at the top of the sleeper wall.

Gizzydash · 5 Jun 2021

Would also add the metal nails holding the joists down have basically crumbled to dust, maybe thats a 50 year shelf life thing or moisture levels too high, not entirely sure but adds to my thoughts about needing more ventilation.

oldbutnotdead · 5 Jun 2021

Nice to see a floor void not full of cr*p from doing a knockthrough...
Def make some holes in the sleeper walls, add airbricks at the other end if possible, insulate (you've got room for rockwool supported by netting, you'll get payback inside a year not to mention massively improved comfort and noise levels)
EDIT Maybe stick some noggins between those joists to stiffen the job up

phatboy · 5 Jun 2021

Noggins will stiffen up the floor structure for working on now, but the floor boards or ply will also do it.... ours was the same, a few fell over whilst I was insulating, and they all moved easily.

It should probably have some more ventilation, although it seems to have coped fine without.... and when you insulate less moisture will travel anyway so should be fine. Never hurts to add more vents though. I'd hire a 5" core drill and go through with that.

Patch up or replace the insulation on those pipes too... looks like the cheap one, the Armaflex stuff is much better

Tigercubrider · 5 Jun 2021

To save hiring a core drill couldn't you just remove a couple of bricks and halve them to support?
Or remove a brick or two and stand them on end having removed the stuff inbetween?

AsleepInYorkshire · 5 Jun 2021

I've some thoughts. What are your trying to achieve please?

I think there's an opportunity to increase the floor insulation (various approaches available) but looking at it the floor it seems structurally sound but the odd additional cross flow air brick wouldn't go amiss.

AiY

Gizzydash · 5 Jun 2021

Thanks for the replies. In my head I was thinking considering the timber had been down there for 50 years it was time to change it out, not sure of the lifespan but seems consensus is to keep it although still worried about the 40% + moisture readings on the wall plate.
Would like to insulate but worried about blocking that gap above the sleeper wall that lets air flow around. Not really sure how to honeycomb that sleeper wall as it looks like taking bricks out or part of bricks would weaken it?

Gizzydash · 5 Jun 2021

AiY - just trying to achieve a warmer room above and ensure the sub floor doesn't have any issues down the road with moisture/damp - keep it ventilated and free from any rot etc. Once I sort it and put the finished floor on I want to rest easy there be no issues under there and I don't need to lift it up again for a long time

AsleepInYorkshire · 5 Jun 2021

If you remove the internal sleeper wall and replace the 110mm joist with a deeper floor joist - say 200mm then you don't need to put air bricks is. The added depth of timber joist will allow a greater depth of insulation supported by the deeper joists. I'd suggest you consider PIR which is more expensive but is much greater with thermal efficiency. YOu will have to knock out some of the external sleeper wall to support a deeper joist.

AiY

Gizzydash · 6 Jun 2021

Thanks - so just to clarify, with a deeper joist I wouldn't need the sleeper wall at all? the span of the joist would just be supported at the external wall plates, roughly 3m span, is that right?

Deluks · 6 Jun 2021

Hassle and expense replacing the joists, if you can even acquire the timber in this time of shortages. You'll have to faff about getting it all level again. If it ain't broke....

Just as previously discussed, increase ventilation by removing a few bricks, netting stapled between and some 100mm loft roll between.
I did the same job a couple of years ago, and for piece of mind, gave all the timbers a good soak with timber preservative.

Once the first few floorboards are back down, it will all stiffen up. The weight of the floor itself will keep it all in place, it's not gonna fly away!

mrrusty · 6 Jun 2021

Nothing much to add that hasn't been said already - no real issues there at all. When you put the floor back DO make sure you know exactly where all the services are - it's very easy to forget and punch a screw or nail through.

A Trowel · 6 Jun 2021

As a new floor, you’ll require insulation to current regs and BCO sign off

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Floorboards are up - how do I tackle this?

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