Green Building Forum - victorian suspended floor insulation

victorian suspended floor insulation

bogal2 — Tue, 23 Jan 2024 11:05:33 +0000

Im really sad to hear this forum may be closing as its been a big help to me. Hi, just wanted to run this plan for insulating a suspended wooden floor with a good ventilated crawl space below in a victorian house. Ive had a good read of all the posts on here and still feel a bit unsure

The plan I have is to:
Lift boards
fix 35mm woodfibre boards to underside of joists.
Fix and seal breathable windtightnesss membrane below.
Fill 180mm space between joists with steico zell loose fill wood fibre.
Airtightness membrane on top sealed to perimeter of room with tape.
Replace boards.

Grateful for any feedback.

victorian suspended floor insulation

djh — Tue, 23 Jan 2024 11:14:12 +0000

Posted By: bogal2fix wood to bottom of joists.

I'm not clear what you intend here. What is the product? Are these fixed from above or below? Do they provide continuous cover underneath the joists, and if so what is the windtightness membrane for? If not, what do they do?

victorian suspended floor insulation

bogal2 — Tue, 23 Jan 2024 11:28:07 +0000

I was going to use steico universal wet fixed from below to reduce thermal bridging and hold the loose fill insulation in. Maybe the wind tightness membrane is a bit over the top!

victorian suspended floor insulation

Peter_in_Hungary — Tue, 23 Jan 2024 11:33:22 +0000

Posted By: bogal2fix wood 35mm fibre boards to bottom of joists.

I presume are there so that the steico zell loose fill wood fibre can be poured in as a full fill. But I also don't see the need for a wind tightness membrane if the boards cover the underside of the joists.

I woud use a VCL membrane instead of the top air tightness membrane - to perform both functions.

Edit to say cross posted with bogal2

victorian suspended floor insulation

GreenPaddy — Tue, 23 Jan 2024 14:41:37 +0000

What do the mice think about the wood fibre boards and the loose fill. Are they in favour of it?

victorian suspended floor insulation

bogal2 — Tue, 23 Jan 2024 17:28:41 +0000

I should imagine they would love it as with most other insulation materials or membranes! My wetsuit got eaten in the shed a few years ago, so I don’t think they’re on an organic diet!

victorian suspended floor insulation

djh — Tue, 23 Jan 2024 20:05:52 +0000

Posted By: bogal2My wetsuit got eaten in the shed a few years ago

Perhaps they were just breaking it up to use as nesting material?

victorian suspended floor insulation

tony — Tue, 23 Jan 2024 21:58:24 +0000

I would prefer to see a vb/air tightness barrier in the warm side of the insulation

victorian suspended floor insulation

bogal2 — Wed, 24 Jan 2024 21:52:44 +0000

I was planning on proclima intello for the vb/air tightness under the floorboards.

victorian suspended floor insulation

Nick Parsons — Thu, 25 Jan 2024 10:25:28 +0000

Can I add a bit? Additions are *between asterisks*

Lift boards
*Check masonry and joist ends for moisture*
*If concerned re results (a) investigate source and remedy as necessary/possible*
*If joist ends <20% moisture content but any residual concern re moisture to walls themselves (external and internal) consider using XPS or similar so that wood-fibre cannot 'suck'.*
fix 35mm woodfibre boards to underside of joists.
Fix and seal breathable windtightnesss membrane below.
Fill 180mm space between joists with steico zell loose fill wood fibre.
Airtightness membrane on top sealed to perimeter of room with tape.
Replace boards.

I like the use of Intello and I suspect that the wind-tight membrane below the 'rigid WF is not necessarily required. However if doing without it I would prime and seal the joints in the WF layer. You want to seal perimeters too, of course, which brings me back to the point re any moisture in the sub-floor walls, since the WF will 'suck'. Again, unless you find the walls absolutely dry as a bone I might come back to my XPS idea (tightly sealed) and then seal the WF to that.

victorian suspended floor insulation

bogal2 — Sat, 27 Jan 2024 11:33:16 +0000

Thanks Nick. Just been looking at how Es Tresidder did his Highland passivhaus retrofit suspended floors.It seems really good to me. Can be done from above, cheap eco friendly materials. Less risk than wood fibre exposed to damp.

victorian suspended floor insulation

bogal2 — Sat, 27 Jan 2024 11:34:58 +0000

victorian suspended floor insulation

jms452 — Sat, 27 Jan 2024 12:01:58 +0000

Have you thought of this system to avoid the need to lift the boards?:
https://q-bot.co/

victorian suspended floor insulation

bogal2 — Sat, 27 Jan 2024 15:34:06 +0000

The ground below
is very uneven and would prefer not to use foam. Looks very useful though!

victorian suspended floor insulation

WillInAberdeen — Sat, 27 Jan 2024 15:56:36 +0000

It's a matter of opinion, but my understanding is that the cold soil below a Victorian suspended floor is supposed to act like a dehumidifier for the room above. Moisture vapour from the room, diffuses into the underfloor and either is removed by the through flow of air, or condenses in the cold soil and drains away. So when insulating my suspended floors, I have tried to keep them breathable without a vapour barrier. I see other people using vapour barriers to keep the moisture within the room, in which case the room ventilation needs to be up to scratch or there will be condensation on wherever the next-coldest surface is.

It's like an upside down version of a loft space. Some folks like to fit their insulated ceiling with a vapour barrier, others like to use breathable loft insulation and keep the loft well ventilated.

Either way, the airtightness is important, particularly round the skirting boards, improving this made a big difference to our floors.