Beam and block retrofit insulation

[Tiny]

Hi.

about to start ground works on extension and whole house renovation. Still not resolved how to improve/solve insulating and improving airtightness of existing exam and block floor. House is built on a slope so crawl spica is from 1200mm down to 400mm at front of house. Somewhat unbelievably there is no insulation present! This is a 70's built house, buildup currently is laminate floor, 3mm cork underlay, 50mm screed, beam and blocks. Underside is bare earh with ventilation bricks. House is draughty and cold, never gets above 16deg in winter. We have mains gas ch with reasonably sized radiators for space.

One thought was to dig off the screed and fit 60mm cps and clip ufh pipes to it and use 40 liquid screed. Floor to ceiling is currently only 2200mm so cannot afford to lose much.

Second thought was to treat entire crawl space as part of the house, fit Val over bare earth, fit XPS onto walls down to footings and connect Mvhr to this space and hopefully gradually heat the beam and block up. Place low build up ufh onto top of screed. Also possibly fit EWI to external wall of crawl space, digging to footings and backfilling. Is this a viable alternative to digging the screed up? Or will there be too much heat loss at the edges?

was thinking could knock off internal plaster and edge of screed and fit perimeter insulation around edge of screed where it meets external walls.

 

or has anyone managed to retro insulate a beam and block floor?

 

my trial dig with a lump hammer and bolster to see how the screed came up resulted in two blocks cracked right through, so concerned at how many I would damage attempting to remove the screed. plus it is time consuming.

 

hoping others may have overcome this problem 

 

thanks 

 

Tiny

 

 

 

 

[PeterW]

Welcome ....

 

I’d line the undercroft with DPM, seal the airbricks that are doing nothing to help as concrete doesn’t rot like timber and fill the whole void with EPS beads ..!

 

Quick and simple and will give you lots of insulation ..! Don’t even consider UFH unless you’ve got 100mm of PIR below the floor or you will be wasting heat ...!

[Tiny]

Hi Peter

Thanks for your reply. It is a big void to fill with beads! What do you think of insulating the exterior walls and connecting the underfloor space to MVHR. Would really like to utilise UFH as moving to a more open plan design. So trying to explore all potential ideas to mitigate heat loss. Cannot understand why uninsulated B&B floors managed to pass through BC, but I have to work with what we have. 

[Mr Punter]

Maybe also consider Leca expanded clay beads to fill the void

[PeterW]

3 hours ago, Tiny said:

Hi Peter

Thanks for your reply. It is a big void to fill with beads! What do you think of insulating the exterior walls and connecting the underfloor space to MVHR. Would really like to utilise UFH as moving to a more open plan design. So trying to explore all potential ideas to mitigate heat loss. Cannot understand why uninsulated B&B floors managed to pass through BC, but I have to work with what we have. 

 

Not a hope for the MVHR heating a space - air doesn’t hold enough heat to keep that space warm. 

 

Other option is to wedge a couple of layers of EPS against the bottom of the beam and block - or glue them with low expansion foam - to insulate the bottom of the slab. The downside of that approach is that it needs access to the undercroft for 8x4 sheets of insulation. 

[Tiny]

Hi Peter

Thanks for your comments, was not trying to heat the crawl space with the MVHR, more to keep some ventilation, in a controlled manner.

I have good access to the underfloor space at the moment, it looks like I could fit 50mm of EPS between the beams after knocking off the casting overhangs, this brings me flush to the beam. So could bond 100mm PIR to the beam face and seal as good as poss with foam at joints and edges. I have space to fit EWI to go past the wall/floor interface. Also plan to fill the cavity with eps beads from foundation to beam and block floor level. Do you think UFH is feasible? It would have to sit on top of the 50mm screed, so means heating the whole floor build up. Or will there be too much heat loss down through the floor. Any advice on what grade/spec of plastic sheet g to use for the vapour control barrier onto the soil in the crawl space. Sorry for all the questions, but it is a lot of hours to invest so want to as good a job as possible, I currently have the time to invest.