Floorboards sagging, suspended floor repair/insulation Qs

[jkn]

Hi All I'm looking for information on suspended floor repair and insulation.

We live in a (1950's)? short terraced house on the south coast. We have a long living room due to the house having been extended, a long time ago and before we were occupants.

Recently, part of the flooring on the 'extended' part' has started to 'sag'. This has not been helped by young persons using their 'Hoverboards' indoors! Basically, it feels like some of the floorboards are starting to give way when weight is put on them.

From a bit of reading, I guess that the construction is of floorboard onto piers over a concrete 'slab'. I could be wrong, however. I am presuming that we will have to get the floors redone - at least the extension part, the floor under the original plan part still seems sound.

Some questions whilst I continue to read and research...

1) Any thoughts on whether this is likely to be just the floorboards, or something more serious? I am moderately concerned that most of the work that has been done on this house appears to have been 'Friday afternoon' job. I'm slightly nervous what we might discover in the course of this...

2) How is this floor likely to have been insulated, if at all? I am guessing that it would be worthwhile in getting it done to more modern standards. What would this be likely to mean? I've used Celotex & Rockwool etc. in the loft but am not clear what you'd do underneath a floor.

3) It is possible to lift the original carpet and refit after the work is done? Even if only temporarily, this would be handy.

Thanks for any pointers.

J^n

[The Natural Philosopher]

I would expect a suspended floor to be done over joists and not feature a concrete slab at all. And the joists have rotted

I think, to be honest, that a *proper* job is going to involve taking the whole thing up, and starting from scratch. I.e laying a proper concrete slab, then a load of celotex, then screeding over OR you might do worse than construct new joists, infill with celotex and board over.

Yes, it is.

Bumping a fitted carpet back onto the spiky things is however probably best left to carpet fitters who do it every day.

But if its been glued down, forget it

[Robin]

"beam and block" is still used around here on some refurbishments of Victorian terraces; and was still recognised in Approved Document C last year

[The Natural Philosopher]

Beam and block is not only 'still recognised' it is a no 1 preferred method for new constructions on clay soils. It is far more heave resistant than laying a concrete slab on the ground

[Tricky Dicky]

I would at least lift a few boards and inspect the joists because if you have rot then it may need extensive work especially if it is dry rot less so for wet rot. Dry rot can be identified by white tendrils covering affected timbers. Repair involves cutting back affected timbers at least

600mm beyond the rotted wood and tendrils and disinfecting all surrounding areas of brickwork, in small rooms it is probably best to remove the lot.

Richard

[The Natural Philosopher]

It is nearly always best to do that. There comes a point where remedial work is more labour intensive than a 'strip it all out and start again'. And people who can build new houses are more common than ones who can repair old ones so to speak

[John Rumm]

As a general rule, floors if adequately supported ought not to sag. Which suggests if they are then it might be the supporting bit that has the problem.

Unlikely to be just the boards - or even the joists, unless there is a problem with rotting timber. So getting a few boards up to have a look sounds like the first job.

How long has it been there, and been ok? Substandard work would usually reveal itself fairly quickly.

Probably not at all. If it is on joists, on piers, on a slab, there might be some insulation in the slab - but that is only likely if it is a relatively recent job (say last 20 years)

You can insulate between joists, or slung under them - it depends a bit on how much space you have under them to play with. In some cases you can lift boards, fit rigid panel insulation and lay boards back on top of that (with a corresponding lift in floor level)

Yes that is usually ok, unless it has been bonded to the floor - in which case getting it up tends to be destructive. (some old foam backed carpets also tend to shed their backing)

[Algernon Goss-Custard]

John Rumm [e-mail] posted

I have considered cutting Celotex panels to fit between my joists, and jamming them into the gap (working from below). Would that be likely to cause condensation?

[Chris Hogg]

As a first off, make access to the under-floor space and have a look. It could simply be that the pillars have settled a little and are no longer supporting the joists effectively. If that is the case, get some scrap bits of slate and pack them into the gaps between pillar and joist.

[alan_m]

+1 Possible supported on a low brick wall but installed without a damp proof membrane between the wood and brick.

Are the floor boards sagging at the edges next to a wall (or what used to be a wall)?

Commonplace for suspended wooden floor to have zero insulation

[Andrew]

All the new houses built in my village over the last couple of decades have been constructed using concrete beam and block ground floors that are then overlaid with rigid insulation followed by some sort of semi-liquid screed that sets really hard.

[Jeff Layman]

Ours most certainly doesn't have any. But then where would you put it? And what would be the point of having airbricks if you had close-fitting insulation under any wood?

[jkn]

Hi all - thanks for the varied and useful replies.

A few bits of follow-up information.

- The extension has been here for at least 25 years, and probably a good bit longer than that.

- The reason I think this extension has a concrete slab underneath is that a few years ago I got a 'surveyor' to have a look regarding a (possibly) unrelated issue; we had/have some damp in the corner walls of this extension. He claimed some knowledge of the likely construction in this part of the world, and this was part of his report. I am trying to find my copy of that now... at the time I part-addressed his recommendations by chipping out plaster from behind the skirting boards, to ensure there was a proper gap between the floor and the plaster.

- The failing is not at the edge of the room, but at the centre. This is where the hoverboarding has been taking place! (I think this has just accelerated the fault, rather than causing it).

- Thanks for the comments about carpet removal and refitting. This carpet is properly fitted with grippers etc.

- I think it pretty unlikely that there was any insulation fitted. I guess that can be addressed once we know what is going on. The extension faces down a hill, and I think there is likely to be a bit of room under the floor.

- it does sound as though we need to have a proper look. It does feel as though it is the floorboards themselves rather than any joists, but given my other comments about damp etc. I appreciate it will all need checking.

- currently trying to find the right sort of person to take a look at all of this...

Cheers, J^n

[alan_m]

The free space under my floorboards is approx 2.5 foot. I suppose that I could fit insulation between the joists and still have a foot of free space beneath. When I purchased my current property I was advised to replace the terracotta airbricks with plastic airbricks to increase the airflow beneath my floor.

The only floor insulation I have is 11/12mm foam underlay on thick lining paper with fully fitted carpets.

[jkn]

Well, as some are suggesting, between the joists is one plan.

Shurely the air bricks wouldn't do any harm even if there was close-fitting insulation under the wood (given sufficient room)?

[Andrew]

If you can get under the floor (reasonable crawl space) then fitting rockwool between the joists held in place with galvanised chicken wire is the best compromise between adding insulation while also allowing some air (and water vapour) to migrate through the insulation down into the ventilated space.

[charles]

How do you get there to fix it? Crawl through an airbrick?

[Tim+]

1) Lift floorboards. Lay loose netting over joists. Lay rock wool insulation in the netting. Replace floorboards. 2) As above, but use celotex or similar. 3) Send remote control robot underfloor armed with spray-on insulation.(eg.

There may be other methods, but those are the one I know about.

Tim

[alan_m]

Lift enough floorboards to allow the rigid insulation to be pulled into the gap between joists. The problem areas will be the runs of water, ch and gas pipes and where wiring is routed through the joists.

[Fredxx]

I've seen places with a hatch to allow access. Always useful if you ever want to run cables etc.