Hello there

I'm a newbie so apologies that these questions might sound dufferish (hence the name!)

We have recently bought a late, late Victorian or super-early Edwardian semi. It has loads of original stuff which is exciting but also entails a lot of repairs!

Whilst we're getting some floor joists repaired in one of the ground floor rooms, we're thinking of having underfloor insulation put in. There's only a small crawl space so this will entail having the floor up. For info - the crawl space (from the bottom of each joist to the floor) is 700mm max so, we gather, not enough space to do the job from below (although I went and had a roll around in there last night and found it to be a lovely cave but I guess I wasn't trying to do work!) The room we have so far inspected has a clear void and we've already cleaned 110 years of dust out of the vents which sit at joist-level.

We've found a builder who seems to be sensitive to old buildings and green measures (he's done a lot of church renovations, apparently) and he seems good to work with. We're not sure about the spec that he's proposing for the underfloor insulation though so it would be wonderful to get some views on the specifics so that we can have a more sensible conversation with him.

He's proposed what seems to be the usual insulation between the joists but with some additional flourishes which we're curious about. This is his proposed construction:
Chicken-wire between joists holding some kind of insulation TBC (we will insist breathable, hygroscopic etc) with building paper on TOP of the joists and then on top of that wpb weyrock flooring and then, optionally, floorboards. To accommodate the added layer of Weyrock he plans to cut off the bottom 18mm of the skirting boards.
There are a few things which are worrying us a bit about his spec:

(1) He's proposing to get rid of the floorboards and replace with wpb weyrock flooring which seems to be a moisture resistant chipboard. To be fair, the floorboards are only original in around two thirds of the room - the other third is not original and the replacements don't match. The room is, in any case, carpeted at present and will stay so for the foreseeable. His other suggestion is to put in the chipboard and then add the floorboards on top, slicing the bottom off the skirting board. We've been reading around this and haven't really come across chipboard before in this application. --> Our question is --> How beneficial is the chipboard? Would it be madness to have the work done and not add the chipboard? Is there anything we could use in place of the chipboard that would be less deep (and thus take away less skirting)? If the chipboard is to reduce drafts, can we instead seal?

(2) We have another couple of downstairs rooms which we're tempted to have insulated at the same time but in those rooms, the floorboards are exposed but not original, we think - we'd love to stick with exposed floorboards in this room but if we could reinstate something a bit more like what might have been here before, that would be a bonus. I'm particularly precious about the skirting boards being reduced in height as they're gorgeously deep at present. So, here, we're wondering - whether anyone knows of any material that would offer the benefits of the chipboard (whatever they may be, presumably reducing airflow) but with the looks of pitch pine or similar. Probably a pipe dream but if anyone is going to know, it's going to be you people, by the looks of things!

(3) He's proposing to use wire mesh between the joists. Most of what I'm reading suggests plastic mesh - are there any issues about wire?

Any experiences, knowledge and suggestions gratefully received.

Thanks for your time.

F

Sounds like a nice house, well worth preserving or restoring original features. Any pics?

A complete alternative to what's being proposed:

Leave the floors completely undisturbed for a start - sounds attractive?

Outdoors, dig a trench all around the perimeter, down to base of foundatioin but not an inch further. Assuming that's at least 750mm below GL, fit 150mm expanded polystyrene (EPS) insulation boards against the wall face and over the enlarged base strip (which is often just a belling-out of the masonry above). Put a french drain (perforated flex drain pipe) right at the bottom, so any water dropping into the ditch gets drained away - hope you can find an outlet for the drain water, to surface-water manhole or just discharging over a descending garden slope). Backfill the trench with LECA (Lightweight Expanded Clay Aggregate) which is like little hard malteser balls of fired clay and forms a perfect free-water-flow medium (catching water and dropping it down to the drain) and also has decent supplementary insulation value (about one third that of EPS) given its greater thickness. Top that off with topsoil, paving or whatever. Plus you need to 'wrap' the LECA in Terram or similar water-permeable geo-textile to prevent fines from gradually clogging up the interstices of the LECA.

What this achieves is a downstanding 'coffer dam' of insulation all around the house perimeter - which drastically reduces heat flow dopwn through the floors, turning outward through subsoil and foundation wall and coming up to stone cold surrounding surface. It forces such heat flow onto a much longer path down, out under the 'coffer dam' and back up to the surface. At that 'thickness' (path length) subsoil actually is quite adequately insulative. Heat flow 'straight down' (as opposed to down/out/up at perimeter) soon (prob already in your case) stabilises at a low level so is not the problem.

The french drain also guarantees your foundation walls, block of subsoil under the house, and floor timbers, to become bone-dry, thus also ending any rising damp you may suspect.

Thanks so much for all of your comments. It's really generous to send such detailed responses.

I think we're edging, unexpectedly towards the jumpers route as there seems to be much more to this than we'd thought. We're looking at doing a LOT more reading and learning and then MAYBE doing something in a few years.

All the best

Frances