How much to replace a floor if wood has rotted?

RHemmings

While I'm aware that this is a length-of-string problem, are there any wild estimates as to how much it would cost to replace the wood of a suspended floor should it be necessary? Possibly including joists in the worst case. 

I've looked on checkatrade, and I simply cannot believe these low costs. 

https://www.checkatrade.com/blog/cost-guides/cost-replacing-joists-floorboards/

I'm not sure I understand how the costs are working here, e.g. are materials included? But, even if I add the labour to the cost, it seems to contained by the number £1500. Which seems very cheap. Is this missing the cost of materials? 

I've had a recommendation for an inspection by a damp and timber specialist, but quoted £360 for that. I'm going to have a second viewing, but am starting to feel minded to take the risk on this one.

My long term plans for the property include at least under-floor insulation, and possibly under-floor heating. So, there may be economies of labour possible. 

EDIT: These costs of up to about £3200 seem more realistic to me, but that's for a lot of work. Given that this appears to be the biggest financial risk I will take with this home given the initial debriefing from the surveyor. https://tradesmencosts.co.uk/rotten-floorboard-replacement/  I'm minded to take it. £3200 is a reasonable chunk of money, but won't ruin me if I had to do that. 

ProDave

Get a local joiner or small builder to come and give you an estimate.  If the old joists are rotten, you might need some other alterations to stop the new ones doing the same.

Well done for planning to insulate the floors properly while they are being replaced.

lincroft1710

The info is a year old and I'm sure prices have increased over that time. 

RHemmings

Thanks. I only need very rough figures, though I have no idea how much building works inflation has been over the last year. £5000, £10000, £20000, £50000. I only need that sort of level of estimate. It seems closest to £5000. 

I don't know that the floor needs to be fixed. Just that it's a potential concern. The classic case of the FTB being excessively worried about a survey, quite likely. I will pursue a second viewing and will inspect the floor (and the bridging of the good condition damp course that may have caused problems.) If I can't spot anything seriously worrying myself, then I am minded to take the risk. Which is only a risk, not a definite problem. I don't mean to over-rule the surveyor who knows much more than me, but would feel happier taking the risk if I have had a look myself. I also want to look at the issues (front steps, path, boarded area) with the damp course and blocking of one underfloor air brick. 

Novice_investor101

10 years ago when I bought my house the survey said to instruct a damp & timber & roof survey. There was extensive rot to the living room floor above the cellar & the floor was dropping in one corner. I’m pretty sure that extra survey cos about £350 then & it recommended fully replacing the floor at a cost of £2600 (back in 2013). I had that amount knocked off the purchase price. Flooring got replaced along a load of other building work at the same time. 

35har1old

RHemmings said:

While I'm aware that this is a length-of-string problem, are there any wild estimates as to how much it would cost to replace the wood of a suspended floor should it be necessary? Possibly including joists in the worst case. 

I've looked on checkatrade, and I simply cannot believe these low costs. 

https://www.checkatrade.com/blog/cost-guides/cost-replacing-joists-floorboards/

I'm not sure I understand how the costs are working here, e.g. are materials included? But, even if I add the labour to the cost, it seems to contained by the number £1500. Which seems very cheap. Is this missing the cost of materials? 

I've had a recommendation for an inspection by a damp and timber specialist, but quoted £360 for that. I'm going to have a second viewing, but am starting to feel minded to take the risk on this one.

My long term plans for the property include at least under-floor insulation, and possibly under-floor heating. So, there may be economies of labour possible. 

EDIT: These costs of up to about £3200 seem more realistic to me, but that's for a lot of work. Given that this appears to be the biggest financial risk I will take with this home given the initial debriefing from the surveyor. https://tradesmencosts.co.uk/rotten-floorboard-replacement/  I'm minded to take it. £3200 is a reasonable chunk of money, but won't ruin me if I had to do that. 

Is it wet or dry rot

RHemmings

35har1old said:

Is it wet or dry rot

It's not known if there is any rot at all. One air brick is blocked which might make the underfloor damp, and the building had reasonably high levels of damp, but not visible. That could be due to the damp course being breached, which it is in several places. 

It's a matter of whether to take the risk on the floor or not. It is only a risk, not a known problem. 

I've been thinking about it, and because of various other things - like I will have the problems with the damp course being breached fixed, and I intended to expose the floor to insulate it at some point, if not install underfloor heating, I'm thinking it might be an OK risk to take. 

Novice_investor101 said:

10 years ago when I bought my house the survey said to instruct a damp & timber & roof survey. There was extensive rot to the living room floor above the cellar & the floor was dropping in one corner. I’m pretty sure that extra survey cos about £350 then & it recommended fully replacing the floor at a cost of £2600 (back in 2013). I had that amount knocked off the purchase price. Flooring got replaced along a load of other building work at the same time. 

I know it's a risk, but it's only a suspicion that there is a problem down there in my house. I don't think I can buy a house without risk, and given that I plan to be doing something with the floor in 2024 sometime, I'm tending towards taking the risk. 

ThisIsWeird

If you will be lifting enough of the floor in order to run pipes, cables, etc, and add insulation (great idea), then you'll be paying for the labour cost for this in any case. 
Should you then find 'rot', the chances are (but by no means certain, of course) that it'll be limited to some joist ends, and possibly the floorboards immediately above them - very limited damage. In which case, the cause obviously needs to be sorted, but the actual repair - cutting away all affected parts, treating the rest, and screwing/gluing new joist extensions on - is relatively minimal. 
If this is the original house construction, and it clearly has a foundation void (albeit somewhat compromised by covering a vent), then you'd have to be extremely unlucky to find extensive rot - it just hardly ever happens.
If it's a more recent extension, then it could be more of a lottery, unless you know how it was built. (Bro bought a Victorian terraced house donkeys ago which had an extension that was slowly detaching itself. Floor there was clearly soft too. Lifted floorboards, and found joists had been laid directly in the soil )