Suspended timber floor

[Oldcellar]

Hi all, firstly thanks for the tips I have already received reading the forum its very informative!

I recently bought a grade 2 listed end of terrace house and am looking to bring it up to standard. Generally its OK but previous owners seem to have been bodgers or people who do nothing at all, not even maintenance.

This question was focused on our suspended timber floor in the front room. The front half of the house has this floor with the back half being a cellar. The floor only has one air brick, and I can't see any evidence of others being covered or removed. The space is dry so it seems to be working but should I look to put another in?

I would also like to insulate the floor but am concerned about ventilation. The construction has 2 sleeper walls which are solid, ie no honeycomb or other ventilation aids. The air can get to the back of the room through the gaps between the wall and the boards as the joists are approx 10cm high. I could reduce the insulation thickness in this area or put holes in the sleeper walls. Has anyone done this before, how did you approach it?

 

[Cubist]

Hi There and Welcome to the Club,

As I am sure you have already found, there are many rules associated with maintaining a period property; and particularly the listed variety.

One of the Golden Rules though is - if its not broke don't fix it.

If there is no evidence of damp or wood rot of any kind then in all likelihood another air brick will not produce any benefit. That said, I have no experience of insulating a floor space and therefore do not know what the ventilation impact may be, hopefully other members will be able to contribute some thoughts on this for you.

Cheers,
Cubist

 

[88v8]

Another air brick would do no harm, although as Cubist says it may do no good.
I presume the sleeper walls are single skin. So you could carefully knock a couple of bricks out to improve the ventilation. Being laid in lime, they'll probably come out quite easily.

To insulate you'd have to take up a lot of the floor for access. Then you could suspend poly bats on wood fillets between the joists. Or suspend loft roll on nylon netting between the joists. I wouldn't put the insulation under the joists.

Having said that, the heat loss through a wooden floor is very low. Less than 10% of the total. Unless you're taking up the floor anyway, I wouldn't bother. It won't be cost-effective and you won't notice the temperature difference.

What do you intend to do with the floor? Stain it? Or cover with lino, carpet? Is there any sign of how it was finished originally?

If you want to stain it and it's tg (tongue & groove), fine; tg is airtight. But if the boards are just butted and have shrunk so the wind is whistling in, then forget about staining them!! By the time you take up the floor to make the underside airtight, the boards will be so mangled it won't be worth staining.

In that case, lay hardboard over the floor, cut it accurately to the skirtings, nail all over with ring nails at 9" centres. Now you can lay lino &/or carpet. Fitted carpet is not Period, but underlay + carpet is a pretty good insulator.

Before hardboarding, be sure you won't want to take the floor up again afterwards, no second thoughts about wiring or plumbing.

Ivor

 

[MatthewC]

The suspended floor in my listed stone built house had only one vent (in the front wall) which was cunningly blocked with a lump of cement on the inside, so only found when I did the floor which was quite poor near the edges.

When I replaced the open fireplace (having accidentally broken the old 'orrible concrete one! Honest!) the installers said that regulations required a vent to the already draughty room and they were going to put it in the front wall'; I said "how about one in the floor?", and they proposed a position near the front wall; I said "how about the far side of the room?" Thus we sited it near the back of the room which then ventilates the entire floor space as well as satisfying the regulation.

Although you might not think the floor space is damp, I reckon that such a vent will prevent any unseen dampness and so is much better for the life of the floor.

 

[Flyfisher]

When I replaced the open fireplace (having accidentally broken the old 'orrible concrete one! Honest!) the installers said that regulations required a vent to the already draughty room and they were going to put it in the front wall'; I said "how about one in the floor?", and they proposed a position near the front wall; I said "how about the far side of the room?" Thus we sited it near the back of the room which then ventilates the entire floor space as well as satisfying the regulation.

We had a similar thing when replacing an open fire with a stove in a room with a suspended floor, though I understand that additional vents (of a prescribed area) are only necessary for stoves rated at more than 5kW.

We sited the vents on each side of the fireplace on the basis that the stove would draw air through the new vents in preference to the usual draughty places (under doors, sash windows etc) and we didn't want cold air being drawn right across the room. The installers were quite happy to place the vent anywhere in the suspended floor.

As for the OldCellar's floor, I tend to agree that an additional airbrick will likely make little difference (unless, perhaps, it could be inserted in another wall and therefore increase air circulation due to the wind causing slight differences in pressure around the property) but it does sound essential not to block the airflow over the sleeper walls when adding insulation. If that gap between the sleeper wall and the floorboards must be filled with insulation then an equivalent area should be opened up within the sleeper wall to restore the ventilation as it currently exists.

 

[Dumsey]

Hello, I am another new member and would also like to thank you all for the interesting information on this forum.

I have a stone house, built around 1890, with suspended timber floors and a cellar running under the front two rooms. The floors always feel cold (despite having underlay and carpet on them) so I was thinking about putting insulation below the boards, between the joists. The cellar is very well ventilated with airbricks, two hearths and old back-filled windows -Yes there is even still glass in one of them! My concern is that I hope to be able to afford to install a multi-fuel burner in one of the rooms next year and reading this, I am now wondering if the combination of that and the insulation would not be a good mix.
What would you all think?

 

[88v8]

.... with suspended timber floors and a cellar running under the front two rooms....
I hope to be able to afford to install a multi-fuel burner in one of the rooms next year...

Hello and welcome.

As a general comment, it's always better to start your own thread rather than piggy-back onto someone else's, as the responses become confusing.
But as you're here......

So you can get at the floors from underneath? You don't have to take them up? In that case, yes, slip some insulation under, loft roll would be fine, and then board beneath the floors - ie the cellar ceiling - with, ummm, matchboard? That would look reasonably 'Period'. No need to paint the matchboard, it will tone down in time. Fix it with brass pins by secret nailing.
Run the boards under the joists, as with a normal ceiling. The difference from the OP's situation being that you have the headroom and the ventilation.

Stove... not sure where you're coming from, how might that be a problem? Are you thinking that the stove could meet the ventilation requirements by drawing air from the cellar? OK, so cut a couple of brass vents into the floor near the fireplace and don't cover them when you insulate and board the cellar ceiling. The vent requirement, iirc, is one square inch per kw above 5kw.

Note that the vent requirements are only sufficient to keep the stove from killing you with CO. They do not guarantee that the stove will burn happily. For that it needs a decent air supply, either by natural ventilation via 'draughty' Period windows and doors, or if the house is sealed up tight by modern windows, then via a decent size vent.

Multi-fuel, btw, if you intend to burn smokeless fuel you need a 904 liner - the cheaper 316 is not adequate for the corrosive combustion products of smokeless fuel.

Ivor

 

[Dumsey]

Apologies for piggybacking. Also many thanks for your helpful reply. Yes, I can get under the floors and will follow your advice re: vents