Internal insulation on external walls and floor

snout71

I have a large Edwardian property, solid brick, which previous owners had external insulated rendering put on outside walls. House is still draughty, can hear traffic outside through the walls and expensive to heat.  I am after solutions that I can DIY internally to make the house warmer.
looking at PIR plasterboard on external walls internally, would I be ok to dot and dab over the existing plasterboard or maybe expanding foam with fixings? I see no signs of damp anywhere but at the same time I dont want to cause any. 

Flooring wise I have no access underneath, I could rip up the flooring from inside but I wonder if I could just lay some ecotec foil/foam insulation ABOVE the floorboards? And seal around the edges to the bottom of the wall to stop the draught coming through. The air bricks are very close to the level of the floor so insulating between the joists under the floor board might not be an option
thanks in advance

FreeBear

Slightly more modern property than yours (late 1920s build) with a mix of solid and cavity walls. When I took on the place, draughty as hell and difficult to heat.

Sealing the perimeter of the room at floor level killed the draughts coming in at skirting level - Used a can of expanding foam, the type with a bendy bit of pipe on the end as a nozzle. Big mistake...

Covered the floor with a layer of aluminium foil (BacoFoil, the wide stuff for turkeys) and then a layer of 5mm woodfibre laminate underlay. Topped off with 11mm foam underlay (should have used 10mm) and a decent carpet. No more draughts coming up through the floor

Windows had nasty cold draughts coming in around the edges of the frames, and hinges/seals were worn out, so another source of draughts. Short term fix was to apply expanding foam to gaps around the frames (used a foam gun this time - much easier to lay down a small bead and get the stuff right in to a gap).

The old heating system went from being useless to managing to warm the place up..

Shoved loads of extra insulation in the loft, going from ~200mm to over 300mm - Low cost with noticeable gains, so worth doing.

Eventually replaced the old 1970s aluminium/timber framed double glazed windows & crappy old front door. Made sure the frames were well sealed around the edges. No more cold draughts, and the heating system started to actually heat the place up rather than just getting it warm.

Have been taking ceilings down in rooms upstairs and packing 100mm of insulation between the joists and making sure it goes right up to the exterior walls. Some of the outer walls have also had 65-75mm of Celotex added, but I don't think it has made a huge difference to keeping heat in. Loft insulation, high performance glazing, and killing those nasty draughts did more.

With your property, I would concentrate on blocking off the draughts and improving the windows & exterior doors. Depending on the windows/doors being period features, secondary glazing would be one option to look at. If you have timber trim around the reveals, pop it off and get the foam gun out to seal gaps between frame & brickwork. Oh, and whack a load more insulation in the loft.

The amount of energy you save by sticking insulated plasterboard on the walls is unlikely to pay for the materials. If you are paying someone to do the work, you're not going to see a return on the investment in your lifetime. With solid brick walls, you also need to be selective about the materials used. Cork & woodfibre boards with a lime plaster will help to maintain the breathability of the walls. Using materials like PUR/PIR (Celotex) runs the risk of trapping moisture in the walls, leading to major problems in the future. Depending on what has been slapped on the outside of the walls, maintaining breathability could mitigate poorly specified external render.

snout71

I have added more loft insulation, not that there’s much loft in mine as it was converted. Upvc windows I have drilled holes in the wood side panels and injected expanding foam around the reveals as there was a cavity of about 3-5cm. Front door replaced for a composite. The idea of the floors sounds good so I will try that out, regarding the Celotex panels, I am unsure I would struggle with damp because the external walls already insulated, though I might not see as much of a return

Albermarle

Could be useful to post how many bedrooms; approx m2; approx heating/gas bill and how long the heating is typically on ( is there someone there all day/most days for example)
You could get some feedback on how expensive the bills are/what you should expect.

snout71

Albermarle said:

Could be useful to post how many bedrooms; approx m2; approx heating/gas bill and how long the heating is typically on ( is there someone there all day/most days for example)
You could get some feedback on how expensive the bills are/what you should expect.

6 bedrooms on 3 floors, 271 square meters. Currently using 40,000 kWh has a year, someone home 24/7 heating on 6am - 10pm averaging about 19.5 degrees. (This gas bill is between 2 houses so probably less than half of this as other house has no cavity wall insulation which is being corrected)
having more solar panels installed so will have about 13kw panels and 40kw of battery storage. Have been upgrading the insulation bit by bit and looking at having heat pump installed once I get insulation of walls and floor sorted.
gas/electric bill used to be 1200£ a month, down to £638/month in November of last year, now looking at probably £3/400 atm with gas being 4x my electric bill

snout71

I’ve lifted up the carpet in front room and they’ve laid chipboard above the joists, but left a 2-3 cm gap between the walls and the outer walls, no wonder it’s draughty, can see the air brick 🤦‍♂️ 

FreeBear

snout71 said:

I’ve lifted up the carpet in front room and they’ve laid chipboard above the joists, but left a 2-3 cm gap between the walls and the outer walls, no wonder it’s draughty, can see the air brick 🤦‍♂️ 

Would be as well to lift that nasty chipboard. If you can get the skirting off the walls without damage, even better.

Put 25mm Celotex between the joists, cutting it so that you get a good tight fit. Screw/nail batten to the joists to support the Celotex so that it is flush with the top of the joists. Squirt expanding foam in to the gaps where it meets the brickwork. Relay the floor, ideally with T&G planks rather than chipboard.

Will kill the draughts, and the Celotx won't compromise ventilation in the sub-floor void. You'll dramatically improve heat retention.

jj_home_80

PIR plasterboard is a good option for internal insulation, but dot and dab might not be ideal if you're fixing over existing boards—mechanical fixings plus adhesive (or even battens) would be better to avoid gaps and ensure a solid fix. Just be mindful of thermal bridging and maintaining ventilation to prevent condensation.

For flooring, foil-backed underlay over floorboards can help, but sealing draughts around the edges is key. If you can’t insulate below, thick rugs or a floating insulated floor (like rigid insulation with plywood on top) might be worth considering. Just be careful not to block airflow from the air bricks.

Albermarle

snout71 said:

Albermarle said:

Could be useful to post how many bedrooms; approx m2; approx heating/gas bill and how long the heating is typically on ( is there someone there all day/most days for example)
You could get some feedback on how expensive the bills are/what you should expect.

6 bedrooms on 3 floors, 271 square meters. Currently using 40,000 kWh has a year, someone home 24/7 heating on 6am - 10pm averaging about 19.5 degrees. (This gas bill is between 2 houses so probably less than half of this as other house has no cavity wall insulation which is being corrected)
having more solar panels installed so will have about 13kw panels and 40kw of battery storage. Have been upgrading the insulation bit by bit and looking at having heat pump installed once I get insulation of walls and floor sorted.
gas/electric bill used to be 1200£ a month, down to £638/month in November of last year, now looking at probably £3/400 atm with gas being 4x my electric bill

Approx 18,000 KWh of gas for heating ( and hot water?)  a 6 bed, three floor, 270 M2 property is quite good considering it is an older property and it is on most of the time. 
It is pretty much in line with the figure used by Ofgem for a typical large property.
No doubt you could decrease it but it is not excessive now. 

snout71

Albermarle said:

snout71 said:

Albermarle said:

Could be useful to post how many bedrooms; approx m2; approx heating/gas bill and how long the heating is typically on ( is there someone there all day/most days for example)
You could get some feedback on how expensive the bills are/what you should expect.

6 bedrooms on 3 floors, 271 square meters. Currently using 40,000 kWh has a year, someone home 24/7 heating on 6am - 10pm averaging about 19.5 degrees. (This gas bill is between 2 houses so probably less than half of this as other house has no cavity wall insulation which is being corrected)
having more solar panels installed so will have about 13kw panels and 40kw of battery storage. Have been upgrading the insulation bit by bit and looking at having heat pump installed once I get insulation of walls and floor sorted.
gas/electric bill used to be 1200£ a month, down to £638/month in November of last year, now looking at probably £3/400 atm with gas being 4x my electric bill

Approx 18,000 KWh of gas for heating ( and hot water?)  a 6 bed, three floor, 270 M2 property is quite good considering it is an older property and it is on most of the time. 
It is pretty much in line with the figure used by Ofgem for a typical large property.
No doubt you could decrease it but it is not excessive now. 

Yes and hot water too. I honestly cannot say whether it’s half or 2/3rds or whatever as the gas line is shared between th3 two properties, I know the main house is EPC of C, and the smaller 2 bed property has no cavity insulation but that’s about it lol. Internal walls are double plastered (maybe to hide imperfections? And has external insulation, but draughty is terrible from floor, I suppose the gas usage in main could be anywhere between 18,000 - 30,000 I have no way of knowing.
main has hot water tank and gas boiler, smaller house has combi boiler, not much use for hot water there

FreeBear

snout71 said: I honestly cannot say whether it’s half or 2/3rds or whatever as the gas line is shared between the two properties,

A G4 gas meter can be purchased for £60-70 (go for an old fashioned mechanical one and then there are no batteries to change). A Gas Safe engineer could fit it in less than 30 minutes.. Should this second property be rented out, having a gas meter in place ensures that you can accurately bill the occupants for their usage.