Hello,

Im looking for further advice on how best to proceed with insulating a suspended timber floor.

So far, the suggested have been:


1) insulated slab

we have around 500mm void beneath the floor. i understand we would need to build the level up with hardcore then something like sand > DPM > PIR insulation > concrete > Screed > finished floor?

Would there be any issues with this method given the depth of the void?


2) PIR insulation between joists

The joists are only 50mm and most people suggest 100mm PIR. Could extra timbers be fixed to the joists at the counter batten points so allow for 100mm insulation?

3) lay new flooring on top of existing flooring.



Would there be much difference between options 1 & 2 in terms of heat retention? obviously there would be a difference in price!

Would option 3 work be any good if new floor was laid with adhesive and sealed at the skirting boards?


sorry i realise there are other threads in a similar vein!

thanks in advance

Fill the whole void with something insulating and non degradable, my choice would be platinum eps beads or if concrete eps sheets under a slab

Thanks DJH and Tony. Food for thought.

DHJ - are you suggesting i could fasten all of the boards to the underside of the joist? like this

U U U U
--------------------

as i have around 50cm of space beneath the joist but no access hatch. I think it would be easier to batten then fit the insulation from above.


Both - could the EPS beads present damp issues and would the beads be filled to finished floor level?


Tony - given the choice would you go beads or slab?


thanks again.

Option 1) it is for me. Next week our suspended wooden floor is going to get ripped out, the 370mm void filled up with EPS, and screeded over with UFH pipes embedded.

I considered filling the void with beads, but I did not want to worry about dampness/humidity migration issues for the coming decades. There are a couple of joists that have become spongy due to condensation on a gas pipe entering the house, and probably also a dodgy soakaway. Addressing these means lifting the floorboards and replacing those joists anyway, so then we are halfway there already.

You need to decide whether to use your local council building control service or a private firm. Whichever you choose, or more than one if you wish, the first thing to do is to phone them up and have a chat. Describe what you're going to do and ask them what will be involved from their point of view, and of course what it will cost. It will probably be helpful to have some drawings and ideally a specification to give them. You can also do it online if you prefer.

Make your mind up which service to use, get them to confirm in writing what they are expecting you to do, and go from there.

Costs are not standard - they are decided by each council or company. There are some example prices online, e.g. https://www.wigan.gov.uk/Resident/Planning-and-Building-Control/Building-control/Fees-and-payments.aspx that will give you an idea of the likely magnitude.

edit: there's a guide to the process at https://www.labc.co.uk/homeowners/5-steps-building-regulations-approval?language_content_entity=en

Do ESP boards help you see into the future?

Victorian floors or suspended floors in modern properties could be included within the heated envelope and made solid by insulating the space above the ground to the underside of the floor with a blown expanded glass bead above a membrane. This arrangement does not then require ventilation to the exterior.

We have used a recycled, expanded glass insulation similar to polystyrene in a bean bag (6-8mm), which can easily be blown or is pourable into cavities or irregular spaces around joists, cabling, pipes etc.

The glass material has excellent insulative values - thermal conductivity in W/(mK-) 0.0661, is inert, fireproof and free draining with minimal moisture absorbency and is free from rot, attack by insects, performance degradation or settlement with time.

We brought in a significant quantity from Europe and have some remaining product from our self-build in Norfolk available for sale.

Apologies, not trying to upset anyone by my use of the same message - just a lack of time available with completing a low carbon self build and the desire to sell our residual glass beads to someone who might be able to make good use of them.

If people are considering the use of EPS between joists then the recycled glass beads offer many advantages. Also, if people have a situation with cables and/or pipes in the voids they are looking to insulate, then the glass beads are free-flowing, making full-fill more achievable.

We were allowed to fill our cavity below our suspended floors fully and the whole is included within our envelope - building control did not question this on our planning application, SAP calculations etc and the foundations and floor slab signed off accordingly. However, we can only speak from our own experience.

We have an MVHR outlet in a recessed plant room which will include warm air heating when necessary, so effectively it will be heated when there is a requirement within the house but with more than 0.5m of compacted glass aggregate and Foamglass boards and glass beads filling any voids, this should not be often. I say will, as we have yet to complete our self-build!