Loft Insulation Upgrade Worth it from about 100mm (Partly Compressed)?

[woodpeckerx]

I know about the diminishing returns on loft insulation but trying to make as many thermal improvements as possible. Burning over 80kWh of gas per day to maintain 17.5 deg C in this cold weather! Windows are UPVC double glazed but 1987 vintage so probably not helping.

One section of loft (16m2) is boarded, underneath the board is 100mm Knauf Glass Mineral Wool on top of the old fibreglass (flat as a pancake) compressed into the 70mm space.

I want to keep this area boarded and not too high, is it worth the cost of adding 100mm PIR on top or will it only give minimal energy savings?

 

[omph]

I know about the diminishing returns on loft insulation but trying to make as many thermal improvements as possible. Burning over 80kWh of gas per day to maintain 17.5 deg C in this cold weather! Windows are UPVC double glazed but 1987 vintage so probably not helping.

One section of loft (16m2) is boarded, underneath the board is 100mm Knauf Glass Mineral Wool on top of the old fibreglass (flat as a pancake) compressed into the 70mm space.

I want to keep this area boarded and not too high, is it worth the cost of adding 100mm PIR on top or will it only give minimal energy savings?

The latest standards recommend 400-450mm of mineral wool insulation. 100mm isn't enough. Fix draughts too, change gaskets etc.

 

[woodpeckerx]

The latest standards recommend 400-450mm of mineral wool insulation

I know, but standards and real world savings are very different things, if £300 of PIR would save me £50 per year I won't bother, if it saves me £300 a year I'll do it. Any idea of the potential saving going from 100mm mineral (compressed into 70mm), to that plus 100mm PIR which would be equivalent to about 270mm mineral over this 16m2 area?

Fix draughts too, change gaskets etc.

Been doing alot of foaming trying to reduce draughts, windows have flipper type gaskets, not sure if worth changing or with the windows being such a vintage (1987) would the glazing be very inefficient?

 

[mikeey84]

They say the average house can save £200-£300 going from 0 to 270mm.

Now the law of diminishing returns applies, so even that 70mm will be doing quite a bit, so the saving is likely to be lower.

I reckon you would save 100-150 per year.

Probably cheaper to fit loft legs, but a lot more work

 

[woodpeckerx]

Probably cheaper to fit loft legs, but a lot more work

I'm going for loft legs for the storage areas with circa 270mm fill of mineral, its just whether to do anything with the central 16m2 boarded section or whether I would be better off concentrating on other areas first?

House is pretty cold, bedroom above garage is down to 13 deg C, had all the floor up and made sure floor void between garage is filled with mineral wool, foamed all edges from under floor and in garage with fire foam, seem to be making little progress but difficult to tell with temps below zero all day

 

[omph]

I know, but standards and real world savings are very different things, if £300 of PIR would save me £50 per year I won't bother, if it saves me £300 a year I'll do it. Any idea of the potential saving going from 100mm mineral (compressed into 70mm), to that plus 100mm PIR which would be equivalent to about 270mm mineral over this 16m2 area?



Been doing alot of foaming trying to reduce draughts, windows have flipper type gaskets, not sure if worth changing or with the windows being such a vintage (1987) would the glazing be very inefficient?

Not sure how large your roof is but £25 for 200mm loft roll in wickes covers 5.6m2. PIR would be prohibitively expensive. Also, it's very hard to get PIR right, making sure it seals properly, wool will do the same with greater margin of error.
Have you checked lighting fixtures ? they usually are quite draughty. Do you have any uncontrolled air flow vents ? might be worth sealing those and investing into a HRV or PIV+heater to deal with condensation.

If you are ripping up floors, then it's worth overlaying them with floor insulation boards, before boarding back up - they will be more effective than mineral wool

 

[woodpeckerx]

Not sure how large your roof is but £25 for 200mm loft roll in wickes covers 5.6m2. PIR would be prohibitively expensive.

Whole loft area is around 90m2, been using that roll and the 100mm in smaller spaces, most of the loft was already covered with about 200mm cross laid 100mm over 100mm only using PIR where gap is very small or trying to keep the height down like this central section.

Have you checked lighting fixtures ? they usually are quite draughty.

Replaced all the upstairs ceiling roses, moved them to room centres, foamed the old holes but not the new holes, they have insulation over them, I will check them.

Do you have any uncontrolled air flow vents ?

No vents at all

Also, 1987 windows, are they single glazed and/or aluminium frame ?

UPVC with double glazing, they actually look in very good condition, hard to believe the age but previous owner left a box with all the receipts.

If you are ripping up floors

Just did bedroom floor above garage, screwed the floor boards back down after removing 750 nails.

Don't know what to do try next really other than upping the heating and paying £600 a month to British Gas

 

[omph]

Whole loft area is around 90m2, been using that roll and the 100mm in smaller spaces, most of the loft was already covered with about 200mm cross laid 100mm over 100mm only using PIR where gap is very small or trying to keep the height down like this central section.

Replaced all the upstairs ceiling roses, moved them to room centres, foamed the old holes but not the new holes, they have insulation over them, I will check them.

No vents at all

UPVC with double glazing, they actually look in very good condition, hard to believe the age but previous owner left a box with all the receipts.

Just did bedroom floor above garage, screwed the floor boards back down after removing 750 nails.

Don't know what to do try next really other than upping the heating and paying £600 a month to British Gas

Modern double glazing has come a long way (Argon gas fill, Low E coating, warm spacers etc). You can get the glazing replaced and keep the same frame if you can't afford a complete overhaul.

Also, how old is your boiler ? how often do you service it ? and have you had a powerflush ?

Does your property have a cavity wall ? or is it single brick/block ? you can get your cavities filled for 700-1000 quid and that will have a substantial effect on comfort/heating.

It may also be the case that your radiators are undersized, and that you need a heat loss calculation and radiators upsized to counteract the heat loss. I would leave this to last.

 

[Old Salt]

To give you a comparison I live in a 2 bed bungalow. 350’ish mm loft insulation, some new DG but some at least 20 years old. New extension but original build is early 60’s and I am using 65Kwh of gas to give 20.5 in lounge and 18.5 to 19 in other rooms. I added additional 100mm of loft insulation this autumn at a cost of about £100.

 

[woodpeckerx]

Modern double glazing has come a long way (Argon gas fill, Low E coating, warm spacers etc). You can get the glazing replaced and keep the same frame if you can't afford a complete overhaul.

I will be doing a complete replacement probably next year so in the "trying to make the best of it phase"at the moment.

Also, how old is your boiler ? how often do you service it ? and have you had a powerflush ?

Think its circa 2006, not a condensing boiler, had it serviced when we moved in 3 months ago which seemed to consist only of hoovering a few dead flies from the casing and measuring the flu gasses.

No powerflush, rads are old, TRVs so old I cannot even get my smart TRVs to fit with an adapter, one rad too small for the room, no fins on back of that one, couple with no TRVs but I've balanced the system as best I can.

Does your property have a cavity wall ? or is it single brick/block ?

Yes, built circa 1960 cavity with the fluffy insulation blown in via holes, 1980s extension is block/brick, original house might be brick/brick but all cavity filled.

It has vaulted ceiling edges upstairs which had zero insulation so I've sorted those at as well.

It may also be the case that your radiators are undersized

One bedroom is undersized but its more about how much gas I want to burn as well.

Trying to find more things to keep the heat in, insulate or reduce drafts etc

 

[woodpeckerx]

I am using 65Kwh of gas to give 20.5 in lounge and 18.5 to 19 in other rooms.

Thanks for the comparison, this is a 5 bed detached, 160m2 of heated space, I've programmed the heating system to come on 9am off at 9pm, heat bedrooms to 18 then target 17.5 during the day with a burst back to 18 between 8pm and 9pm. The largest bedroom is only reaching 16.5 (rad too small) and the one above the garage only about 15 but to be fair not using that one due to the DIY etc

Lounge is around 20-21 all day but have a wood burner topping up the heat, during this cold snap averaging 80kWh gas per day.

Don't know if this is good or bad, had oil before and it was way cheaper than the current gas prices seem to be working out.

 

[omph]

I will be doing a complete replacement probably next year so in the "trying to make the best of it phase"at the moment.


Think its circa 2006, not a condensing boiler, had it serviced when we moved in 3 months ago which seemed to consist only of hoovering a few dead flies from the casing and measuring the flu gasses.

No powerflush, rads are old, TRVs so old I cannot even get my smart TRVs to fit with an adapter, one rad too small for the room, no fins on back of that one, couple with no TRVs but I've balanced the system as best I can.

Yes, built circa 1960 cavity with the fluffy insulation blown in via holes, 1980s extension is block/brick, original house might be brick/brick but all cavity filled.

It has vaulted ceiling edges upstairs which had zero insulation so I've sorted those at as well.

One bedroom is undersized but its more about how much gas I want to burn as well.

Trying to find more things to keep the heat in, insulate or reduce drafts etc

The specs look okay, and you do have a big house. I have the feeling your rads/boiler are probably the core culprit. A 10 year boiler will have around 75-85% efficiency. If you are going to get the windows done, I recommend you upgrade your boiler, and oversize your radiators. The larger the radiator, the lower the running temp because it naturally emits more heat.
I replaced my 10 year old boiler, thought I didn't need it, little did I realise just how much boiler tech has evolved in the last few years. If you can, I highly recommend it.
I have a 5-bed house and use half of what you do. But we have large rads, so I can run the heating at 30c in this weather which keeps the boiler condensing and allows me to run it pretty much 24/7.