Have you considered filling the underfloor void with EPS beads?

Hi Olivia,

pretty much as per DJH above. I'd be less concerned about the VCL under the ply with fixings through. You'll likely be laying a 6mm or 9mm ply to make the floor surface a bit flatter for the finish layer, and so likely fixed with nails/screws every 100/150mm. It will be so well fixed that the VCL will be well held and so pretty good level of air tightness (not perfect). The real weak areas are, as DJH said, around the perimeters, at skirtings etc.

Fitting insulation from underneath a floor is about the worst job you can have, in terms of level of discomfort. I've done this quite a few times, and it's a living hell (but I survived to tell the tale). Here's how I do it, if this is of any help...

Paper suit, dust mask with rubber face seal and filters, rubber gloves under working gloves, goggles (I use swimming goggles). I add a piece of soft sponge material under the mask strap at the back of my head, as that part of the head will be resting on the ground a lot (or your neck will be in spasm after 10 mins). I use a manual Staple gun, but the electric ones aren't much dearer, and will save a lot of hand/arm ache. Stanley knife. Good lighting from 2 directions (stops you creating shaddows). The prep really makes the next hours and days a lot easier.

Assuming the crawl space is quite tight, and will have to slide about on your back, clear out as much debris as possible from the solum (brush it out), spread out a tarpaulin, with another layer of polythene on top. This allows you to slide back and forth, which is much of the work, physically.

Pre-cut the membrane, so you can fill one bay at a time (maybe 2 bays when you get the hang of it). Too much membrane and you just get in a tangle (think wrapping a christmas present, wearing a straight jacket, inside a barrel

The idea is to staple the membrane to the face of the first joist, and have it drooping to hold the wool, and then the membrane comes up the face of the next joist, on the uninsulated side, so you can get in with the staple gun. There will be 2 layers of insulation held up, one between the joist, and the second below the joists.

I start by stapling the first run of membrane, leave it hanging down, fit the first layer of insulation between the joists, which shd stay in place, though sometimes the odd staple at the sides helps. Then push the second layer of insulation against the draped membrane, and tug the membrane towards the adjacent joist, thus holding the wool in place. The membrane will sort of billow, with the second layer of wool being below the joist bottom edge. Wrap the membrane up the outer face of the joist, and staple.

There's a bit of jiggery pokery, and having arms like an octopus would be a blessing, but after a bit you get the hang of it. Repeat the above. You can split each joist bay, so you're not trying to fill the whole run in one go. Just overlap the membrane.

Some would suggest adding clout nails for pull out strength. Good luck with that in a tight space. I usually just double over the membrane to make a hem, so two layers are stapled. You'll use 1000's of staples - don't skimp.

Pipes can be tricky to work around, but can also help by supporting the first layer of insul. The second layer of insul underneath encloses pipes, which is good from a heatloss/frost protection point of view. The wall edges can be tricky, where the joist runs parallel to the wall, with only a small gap. Either shove wool in there, or even rigid insul board cut and foamed in. Which ever you have the patience for. That patience will wane after a day or two down in the pit.

Two people are pretty much essential, so one can cut and pass the wool and membrane in to the other doing the install, otherwise you'll spend the whole time crawling back and forth. Wrap the precut wool in polythene, when it is being passed in, as it will then be easy to drag it through to the required position, and not catch and tear. I use the polythene wrap the wool came in.

I've attached a sketch from a previous project, which is a section through the joists/wool/membrane, and may explain the objective a bit better. Ignore the other wall & loft details. Best of luck. It's torture, but worth the pleasure of a warm floor (and house).

+1

I was assuming that nobody would involve BC unless they absolutely had to, e.g. unless they were doing work that needed planning permission (thus highlighting the project to the Council) or if they wanted some future documentation when it comes to selling the property.
Most people (another total guess here) just want to make their house warmer as cheaply as possible.
I didn't involve BC in my bathroom renovation, but dang we is cozy now upstairs.
No intention of selling any time soon, and even if we did in the future, nobody would care. I guess it's a bad feature of the housing market (location above all else). When we came here, we assumed that nothing would have been done properly, BC inspections or not. Ten years later, I can say that it is a fair assumption. If we want the insulation and airtightness standards any where near that expected by the GBF members, we still have much work to do.

Hi all, please bear with as I'm new and getting the hang of the reply system! :) Thank you all so so much for the in depth responses - it's incredibly helpful!

I would love to fill it and forget about it but unfortunately as it's a bungalow a lot of the wiring and plumbing is done in the void, so we're actually planning on having access hatches to the void so it remains accessible!

The house is on a slope, the deepest end of the void is 5 or 6 feet, the smallest is I think 3 - 4, I'd need to double check. Loads of sleeper walls that separate the void into two halves as well as underneath the house walls.

For taping windows, we'll be replacing the windows eventually as it isn't in the budget at the moment (the glazing is failing quite badly), I'm hoping to work on their airtightness at that point.

I'm hoping to not float the ply but instead screw (countersunk) it to avoid squeaking/any floor issues later down the line. We were hoping to screw the ply through the VCL and into the floorboards, not sure if that'd be okay? VCL would go up behind the skirting board.

@greenpaddy thank you for the details on how to do it from underneath - it's really reassuring to hear it can be done! The membrane you mention, is that the breathable membrane or the VCL (what I mean is do you usually do the VCL from underneath or above the floor? Same Q for the airtightness layer if you have that separate to the VCL)

Thanks again everyone!