Insulate timber floor

[Stonehouse]

Good evening all

Can anyone please advise on how to insulate suspended timber floors?

We’d like to use sheepswool as it is breathable. The following three layers have been suggested:

Breathable membrane
Sheepswool
Vapour barrier

Is anyone please able to offer advise? We have granite walls. Thank you so much!

 

[Feltwell]

You don't really need to worry about breathability on a suspended timber floor - just make sure the sub-floor void is well ventilated to the outside, air bricks on opposing walls ideally. You don't want stagnant pockets of air trapped anywhere.

Have you got access to the subfloor void, is there enough room to get down there or not?

 

[Lacan07]

This is a challenging subject for me in an old house. Apart from everything else I'm a big fan of utilising the original floorboards, any other flooring looks cheap or out of place, and to insulate between the joists means getting up all the boards which will never go back down the same way.

 

[Feltwell]

This is a challenging subject for me in an old house. Apart from everything else I'm a big fan of utilising the original floorboards, any other flooring looks cheap or out of place, and to insulate between the joists means getting up all the boards which will never go back down the same way.

Depends if you're lucky enough to have enough space beneath the floor. I have, there is a (crudely done - previous owner ) hatch underneath one of our sofa's, there's about a 3' high space underneath the joists to crawl about in. So I was able to take rolls of insulation down there and push it up between the joists, leaving the floorboards undisturbed.

But I know what you mean - how you'd get a floor up without damaging many of the boards or at least pulling the nail heads through I don't know. I suppose once you've got a clear start it would help, but on T&G boards like mine I'm sure you'd break most of the tongues off at least.

 

[fernicarry]

If you are going to lift boards then use a multitool to cut the secret nail through the tongues. It won't be fast though and you'll go through a lot of blades. You still need to get started somewhere and that usually involves some damage, but the previous efforts of various trades people have taken care of that for me... You'll run into complications like boards running under internal walls. Its not for the faint hearted.

So far as the actual build-up of the insulation, the membranes are mostly to keep the insulation in place and keep debris out. Insulation clogged with muck stops being effective. I'm not convinced that vapour control layers have any place in a period house but if you did use it then it should be on the side closest to the habitable area, the side against the floor boards. You want to prevent vapour produced inside the property (breathing, cooking, bathing) from entering the fabric, whilst on the 'cold' side you use a breathable membrane to allow vapour and condensation to leave the fabric encouraged by good air circulation in the solum.

Bear in mind that if you block vapour from leaving through the floor structure it will still need to be able to leave some other way (unless you plan on stopping breathing, cooking etc.). This is not usually a problem in period properties as there are plenty of opportunities for air exchange with outside but is why you get those dreadful trickle vents on replacement windows and why high performing modern builds have to use mechanical extraction.

Some good ideas in this for retrofitting from above and below:

https://www.celticsustainables.co.uk/content/Indinature/IndiNature%20IndiThermInstallGuide.pdf

The product itself potentially much cheaper than sheep's wool. I'm going to give it a try on my next project. I have no connection to the company.

 

[Toby Newell]

Good evening all

Can anyone please advise on how to insulate suspended timber floors?

We’d like to use sheepswool as it is breathable. The following three layers have been suggested:

Breathable membrane
Sheepswool
Vapour barrier

Is anyone please able to offer advise? We have granite walls. Thank you so much!

No idea why you would want or need a vapour barrier.

Were you suggested all 3 at once? that makes zero sense, a non permeable coupled with a permeable membrane.

Lifting boards always causes damage. Is this floor ground floor? If so you need to ensure any insulation is incorporated within the depth of the joist so as not to impede the airflow created by the airbricks.

Natural fibres are less insulating than something like polystyrene (Cellotex) or polyurethane (Kingspan), but obviously more breathable. You have to take a holistic approach, if your house is damp or borderline damp or difficult to heat then use natural, if it's toasty, dry and easy to heat then you might want to consider a higher performance man made alternative.

I actually do the work of lifting, repairing and replacing but try to steer clear of insulating. Filling gaps does more than insulating, at least on ground floors as convection is a greater issue. Ideally you want airbrick induced pressure to force moist air through the sides of the house rather than leak up into it. I never advise lifting for insulation on ground floors. On upper floors it makes more sense, especially the top floor, because, physics. Heat rises, hence tea cosys are more popular than tea socks. And thus 'loft insulation' is a commonly known thing and 'basement insulation' is not.

Another point is that airbrick induced airflow helps to remove expired water vapour from ground floor joist, beams and floors better if the vapour isn't impeded by insulation. This is important as unless you replace your entire sub floor many beams / joist in many old properties are set in pockets and or on slates on brick piers and often wick moisture from masonary. To me the benefits of insulated ground floors do not outweigh the costs of reduced airflow to timbers, and considerable extra costs as compared to gap filling, which is over an order of magnitude cheaper. Upper floors do not have this beneficial airflow, often have less 'access' to moisture wicking and will offer a better efficiency return due to them being at a higher temperature than the ground floor.

Forget building regs, some of these, especially new ones are farcical and I have never seen a property built or repaired which hasn't flouted many.

In a new build it is relatively easy to specify whatever dimension insulation you want and factor this into the design and it is a no brainer as the ROI starts from day one. And by ROI I am not simply and crudely referring to monetary cost, but also to 'carbon cost' as the energy and carbon cost of manufacture and installation of the insulation systems are atomised over a potentially greater period. If one is to imagine any new build lasting half as long as many of the properties I work on.

Older properties were simply not designed nor compatible with modern insulation methods or techniques. They need to breathe to maintain the correct moisture level. It's a balancing act. There is an optimum level of 'leakiness' look first at excluding draughts, cheap and effective, then look at insulating the uppermost level, then look at maintaining reasonable heat levels. As someone else said, dry materials conduct heat less than damp ones. Keeping your house heated adequately (maybe counter intuitively) can reduce your bills by reducing moisture levels. Dry walls can effectively double their insulation value and bingo, you just 'insulated' your entire house structure by turning up the thermostat.

Finally look at moisture generation and forced ventilation, bathrooms and kitchens should have fans and windows should be cracked / room heated (maybe with supplementary heaters) when drying clothes. Those with very large houses who have insulated against draughts / fitted double glazed units etc may want to consider a PIV (Positive Input Ventilation) unit, which is basically a thermostatic and hygromatic controlled extractor fan (in reverse) normally fitted to the loft area. This gently forces air and expired moisture out of the building.

These are simply my own thoughts as a highly experienced amateur but who works on period properties for a living. Do your own research but to me lifting timber floors to insulate ground floors seems a very inefficient use of funds and I do my best to proffer that view to my customers.

There is an appreciable problem with new builds that are too air tight giving rise to damp and black mould issues.

You have to strike a balance.

 

[Toby Newell]

Good evening all

Can anyone please advise on how to insulate suspended timber floors?

We’d like to use sheepswool as it is breathable. The following three layers have been suggested:

Breathable membrane
Sheepswool
Vapour barrier

Is anyone please able to offer advise? We have granite walls. Thank you so much!

I got so carried away with my own waffle ( you can tell it's a forced day off) I forgot to concentrate on the OP.

I am thinking granite walls might engender considerable condensation, taking into account my thoughts on my longer post, maybe you might want to consider maximising airflow at (sub floor) ground level.

 

[Apasc]

Good evening all

Can anyone please advise on how to insulate suspended timber floors?

We’d like to use sheepswool as it is breathable. The following three layers have been suggested:

Breathable membrane
Sheepswool
Vapour barrier

Is anyone please able to offer advise? We have granite walls. Thank you so much!

What did you eventually do?

 

[fernicarry]

Since I wrote my original reply I've insulated part of my ground floor. I've written about this in other threads so have a search.

Briefly, its breather membrane stapled under the floor boards and lapped onto the sides of the joists, insulation batts templated to a friction fit pushed up between the joists (Indinature is my weapon of choice at the moment, 80mm thick mostly because its mechanically stiff enough to stay in place whilst you secure all the other bits), wooden slats crosswise to support the insulation resting on battens screwed to the joists and another layer of breather membrane between the insulation and the slats.

The budget version is just the first layer of breather membrane which on its own does a lot to stop air leakage and improve comfort levels. I focus the insulation more towards the external walls particularly around air bricks and under radiators. The materials aren't terribly expensive but its time consuming because every single piece has to be custom made to fit due to the joists not being terribly regular and having been sistered in places.

Do you have access below the floor? IMO its not worth trying to lift a serviceable tongue and groove floor because you'll just be left with matchwood unless you are exceptionally careful and even then there will be some amount of collateral damage. Fair enough if the floor has had it for other reasons. I've done all of it from below which has involved squeezing into some impossibly tight spaces, real buried alive stuff. So far the result has been encouraging enough to keep at it. It goes a lot faster if you have a mate up top cutting materials to size and feeding them down to you.

 

[Lacan07]

One of the reasons I'm not so keen on the idea of insulating under my floorboards is the horrendous thought of having to lift them all with the subsequent potential for damage. The vast majority have been down for over 200 years and fit together perfectly.