Replacing a Victorian suspended timber ground floor

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Hey all

I'm in the process of renovating the living room of our 1900 built Victorian end-terrace.

When I went into the project, I knew that I'd probably find some issues with the floor as there were a few soft spots.
I'd also planned to pull and replace all of the floorboards in order to insulate in-between the joists and install UFH into a 22mm chipboard deck using the Omnie TorFloor system.

However once I've started pulling up the carpet and some floor boards, it's pretty clear we've got some larger issues than I'd thought...

To start with, this was the joist in-front of the now removed fireplace:

This joist runs full length front to back, so just over 3.8m...

And this was the condition of one of the alcove's after pulling some boards up.


Neither of the short joists were secured to anything, and both were pretty rotten as you can see from these 2 photos.



I dug a load of dirt out from around the fireplace in order to get a better look at that first joist, and it's not pretty:


All 4 corners look pretty similar in the state of the joists, so I'm currently thinking the best course of action is going to be to rip all the floorboards and joists out, and fit a completely new floor.
The main thinking behind that is that the current timbers are non-standard sizes at ~70mm x 70mm, so matching is going to prove pretty difficult. And it's probably as much work to replace and match a couple of joists as it is to just replace the entire lot...

So, that leads me onto a few questions.

1. From a quick google, it looks like this will now fall under a Building Notice. Can anyone confirm that before I call Building Control on Monday?

2. Do I need to be getting any kind of structural plans drawn up for the replacement floor?
The floor area is 4.4m x 3.7m, but that includes the bay and alcoves.
Currently, the joists run front-to-back, so the longest will be 4.4m long.

3. There are currently 2 supporting walls at roughly equal distances on the span. I need to measure exact distances though.
However assuming they are equal distances apart, that makes the longest span approx 1.2m, so C24 span tables suggest I can use either 45mm x 72mm or 45mm x 95mm joists comfortably.

I'd like to keep the height build up as close to current as possible, as this room is already higher than the dining room and is semi-open plan thanks to the double door opening.

Finally, has anyone else done this before and have any suggestions, or is there anything else I need to be thinking about?

Thanks in advance for any replies.

Regards
Gavin
 
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lack of through ventilation has been the main culprit causing damage to your floor.

have you considered replacing the suspended floor with a concrete slab over a DPM and insulation floor?
you could even dig deep, & by dropping the FFL, to hopefully level this room with the other rooms?
 
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lack of through ventilation has been the main culprit causing damage to your floor.

have you considered replacing the suspended floor with a concrete slab over a DPM and insulation floor?
you could even dig deep, & by dropping the FFL, to hopefully level this room with the other rooms?

Hey @bobasd,

Ventilation probably is an issue, as I can only see one air brick in the entire room, which is in the bay window.

I hadn't considered replacing with a concrete floor.
Doesn't sound like too much work on the face of things.

Any ideas on a rough cost for an area of this size?

And what would the impact be on walls? As they do show some signs of damp in the alcoves etc. But again, that is probably poor ventilation...

Cheers
 
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So I spoke to the local building control dept' earlier, and they confirmed that as I'm not replacing more than 25% of the total floor area within the building, then it's just classed as repairs, so no need for a building notice! So that saves me one potential headache.

So my next question is: Should I be getting a structural engineer or similar in to design the new floor? Or just do the span calcs myself and layout based on 400mm centres?

Replacing with a concrete floor is I think a bit too far... I'm planning on blocking up the old chimney and fireplace, so I'll include ventilation to the subfloor as part of that. I've also cleared a load of dirt, so hopefully the through flow should be improved.

Comments?
 
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I'm just a diy-er, but my experience is that replacing a suspended timber floor is a relatively simple process, with very simple maths
I did find this helpful:
Some things to consider:
-It's worth digging any rubbish out from underneath, and may be worth digging a bit more out to improve air flow
-If I were you I'd be looking to reuse or sell as many of your existing floorboards as possible
-Ventilation - yes indeed!
 
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although i dont like concrete floors, in your case a slab floor will possibly be a lot cheaper than a suspended floor.
but price will depend on a number of factors.

you will need a min of 150mm space below your suspended floor joists, & venting or air bricks at the rear elevation.
you will also need a min of three air bricks at the front elevaton.
you must have through ventilation from front elevation to rear elevation of the house.
all joist tails must be wrapped in, or sit on, DPC material.

no SE is needed for either floor.

ref chimney breast work or dealing with wall damp - they are best dealt with on here when you have a grasp of whats advised and your searching or similaar threads on here or elsewhere?

the two vids referenced above are OK for Diy'ers who made them but they contain many faults.
 
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Cheers for the responses both...

So currently only the front room is suspended floor. The back room is an un-insulated concrete slab, so venting from front to rear will be pretty much impossible.

So replacing with a concrete slab is looking more appealing.
What's the typical build-up for an insulated concrete floor?

Compacted hardcore (how much?), sand blinding, DPM, 100mm insulation and 100mm concrete, UFH pipes and then 50mm screed?
I'm just trying to work out how much depth I need from FFL, and therefore how much the existing ground level needs to drop by...
 
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google for masses of detailed diagrams - and use the search on here for masses of similar threads.
 
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