Green Building Forum - how much is enough insulation

how much is enough insulation

CJT — Mon, 17 Jul 2023 14:37:14 +0100

As DJH suggested recently this is a question on its own.

Sips Kingspan TEK 142mm with 50 mm extra kingspan on the inside 0.13Wm2K, 150mm under the slab and triple glazed window at .1 W/m2K.

I could still add more inside but dont really want to lose more space. How much is enough ? 1st time build for me so i have nothing to go from. Has anyone done anything similar ? I haven't got my SAPS back yet.

how much is enough insulation

djh — Mon, 17 Jul 2023 15:54:03 +0100

Posted By: CJTtriple glazed window at .1 W/m2K

That seems very unlikely. You might want to check your figures.

how much is enough insulation

Jeff B — Mon, 17 Jul 2023 17:27:01 +0100

I have done IWI with 75mm Celotex. It has made a huge difference to the room warm up time and also in maintaining the desired temperature for much longer. As an example I have attached a temperature versus time plot for our lounge for 30th Nov to 1st Dec last year and you can see that the temperature drops overnight from 22.5C to 19.0C. The heating is on from 7.30 am to 10.00am and then again from 3.30pm to 10.00pm. Before we did the IWI it would typically have been around 17C by the morning at that time of year.

how much is enough insulation

Jeff B — Mon, 17 Jul 2023 17:28:03 +0100

Sorry don't know why it's sideways on!

how much is enough insulation

CJT — Mon, 17 Jul 2023 18:55:21 +0100

Posted By: djh
Posted By: CJTtriple glazed window at .1 W/m2K
That seems very unlikely. You might want to check your figures.

.83 whole window value but i have been working on 1.0 my typo !!

how much is enough insulation

CJT — Mon, 17 Jul 2023 19:01:44 +0100

Posted By: Jeff BI have done IWI with 75mm Celotex. It has made a huge difference to the room warm up time and also in maintaining the desired temperature for much longer. As an example I have attached a temperature versus time plot for our lounge for 30th Nov to 1st Dec last year and you can see that the temperature drops overnight from 22.5C to 19.0C. The heating is on from 7.30 am to 10.00am and then again from 3.30pm to 10.00pm. Before we did the IWI it would typically have been around 17C by the morning at that time of year.
http:///newforum/extensions/InlineImages/image.php?AttachmentID=8600" alt="Lounge data.jpg" >

Internal wall insulation ? I am still learning ! Noticeable difference then. What is the original construction ? Ours will be 192mm of insulation total which i would hope to be enough.

how much is enough insulation

WillInAberdeen — Mon, 17 Jul 2023 21:24:19 +0100

It depends where you are, and how the house is heated. In Scotland, that would be sufficient insulation to meet standards if you have gas and solar panels, or electric heating. In England, electric heating is (bizarrely) penalised against gas heating under the 'Primary Energy' criteria so you might have to go further on the insulation to 'compensate' for not using gas. In both cases you get credit for using a heatpump instead. Other factors include the airtightness and the detailing to avoid thermal bridging at edges. Your design SAP model will balance all these elements together.

From the point of lifecycle impacts, it's worth looking at how much carbon is emitted to manufacture the insulation, which is becoming more important now that less carbon is saved by saving (electric) energy. It might be possible to use less carbon-intensive insulation types, at least in part eg glass wool or cellulose rather than polyisocyanurate. They would need to be thicker.

how much is enough insulation

CJT — Mon, 17 Jul 2023 22:44:14 +0100

Posted By: WillInAberdeenIt depends where you are, and how the house is heated. In Scotland, that would be sufficient insulation to meet standards if you have gas and solar panels, or electric heating. In England, electric heating is (bizarrely) penalised against gas heating under the 'Primary Energy' criteria so you might have to go further on the insulation to 'compensate' for not using gas. In both cases you get credit for using a heatpump instead. Other factors include the airtightness and the detailing to avoid thermal bridging at edges. Your design SAP model will balance all these elements together.

From the point of lifecycle impacts, it's worth looking at how much carbon is emitted to manufacture the insulation, which is becoming more important now that less carbon is saved by saving (electric) energy. It might be possible to use less carbon-intensive insulation types, at least in part eg glass wool or cellulose rather than polyisocyanurate. They would need to be thicker.

Thank you. west yorkshire and possibly ASHP with solar pv on the roof and triple glazing. Realistically money has to be a factor as well. If building as i am doesn't show me benefits in comfort and running cost savings then i will be very disappointed as presently i have found the process to be overly complicated and more expensive than a traditional build with maybe lpg (no mains gas)

how much is enough insulation

bhommels — Tue, 18 Jul 2023 16:40:02 +0100

Another thing to consider is ventilation as part of the insulation strategy.
For example: without heat recovery ventilation there will have to be admission of cold air in winter to keep the indoor climate healthy. This is an irreducible heat loss, which might not be so much of a problem when all other heat losses are much larger. When aiming for a very energy efficient home however, MVHR is more or less a requirement as it would otherwise negate the effect of the high insulation levels.

how much is enough insulation

Jeff B — Tue, 18 Jul 2023 20:25:35 +0100

Posted By: CJT
Posted By: Jeff BI have done IWI with 75mm Celotex. It has made a huge difference to the room warm up time and also in maintaining the desired temperature for much longer. As an example I have attached a temperature versus time plot for our lounge for 30th Nov to 1st Dec last year and you can see that the temperature drops overnight from 22.5C to 19.0C. The heating is on from 7.30 am to 10.00am and then again from 3.30pm to 10.00pm. Before we did the IWI it would typically have been around 17C by the morning at that time of year.
http:///newforum/extensions/InlineImages/image.php?AttachmentID=8600" alt="Lounge data.jpg" >

Internal wall insulation ? I am still learning ! Noticeable difference then. What is the original construction ? Ours will be 192mm of insulation total which i would hope to be enough.

The original construction of the ground floor walls* is (from outside to in) a classical cement render/4" concrete block/approx 50mm cavity filled with loose blown-in Rockwool fibre/4" concrete block, wet plaster. The lounge has two external walls, the other two are internal joining onto the kitchen/diner and bedroom respectively. Obviously we only put IWI on the external facing walls. See schematic diagram attached. Two corrections: we did not use foil backed plasterboard in the end (decided this was OTT as we were also using a VCL) and there are 25mm Celotex sheets between the battens (not labeled as such). All joints in the Celotex were covered with 10cm wide self-adhesive aluminium tape.

192mm of Kingspan sounds massive to me. Have you done a U value calculation?

*It's a dormer bungalow here so the upstairs is a completely different structure with dwarf walls and sloping ceilings (aka skeilings). These have all had the same IWI treatment though â€“ same construction as above.

how much is enough insulation

tony — Tue, 18 Jul 2023 22:02:59 +0100

The op question has several answers, in energy terms or money terms and over what time scale. Some talk about carbon but I see that as a diversion. Then in sustainability terms.

It will also depend on climatic zone too.

I like what is now considered too much insulation as shortly it will be called for, currently recommending 400mm of quilt

I have see it said that 1000mm of fibreglass was sustainable but that was back in the 1980â€™s

I am not sure that there can be too much ðŸ™‚

how much is enough insulation

djh — Wed, 19 Jul 2023 11:06:50 +0100

Posted By: Jeff B192mm of Kingspan sounds massive to me. Have you done a U value calculation?

From the OP:

Posted By: CJTSips Kingspan TEK 142mm with 50 mm extra kingspan on the inside 0.13Wm2K

how much is enough insulation

Jeff B — Wed, 19 Jul 2023 21:52:30 +0100

Thanks djh. I didn't look back to the original post but replied to a subsequent one! So well within the new 0.16 Part L requirement for new builds.

how much is enough insulation

CJT — Thu, 20 Jul 2023 14:41:06 +0100

Posted By: bhommelsAnother thing to consider is ventilation as part of the insulation strategy.
For example: without heat recovery ventilation there will have to be admission of cold air in winter to keep the indoor climate healthy. This is an irreducible heat loss, which might not be so much of a problem when all other heat losses are much larger. When aiming for a very energy efficient home however, MVHR is more or less a requirement as it would otherwise negate the effect of the high insulation levels.

Hi, Yes i am fitting MVHR

how much is enough insulation

CJT — Thu, 20 Jul 2023 14:50:24 +0100

Posted By: Jeff B192mm of Kingspan sounds massive to me. Have you done a U value calculation?

Not done a u value calculation as yet, i am awaiting my Saps survey. Kingspan own figures below for their TEK system showing what can be achieved by adding IWI at various thickness's. I am encouraged by your results it has put my mind at ease somewhat. Thank you.

U-Values for Kingspan TEKÂ® Building System Walls with Various Thicknesses of Additional Insulation and Different Breathable Membranes
Thickness of Kingspan TEKÂ® Building System Panels (mm) Thickness of Kingspan ThermawallÂ® TW55 (mm) Standard Breathable Membrane U-value (W/m2K) Foil Faced Breathable Membrane U-value (W/m2K)
142 0 0.19 0.18
142 20 0.15 0.15
142 25 0.15 0.15
142 30 0.14 0.14
142 40 0.13 0.13
142 50 0.13 0.12
142 60 0.12 0.12
142 70 0.11 0.11
142 75 0.11 0.11
142 80 0.11 0.10

how much is enough insulation

wookey — Fri, 21 Jul 2023 04:39:32 +0100

How much is enough depends on the shape of the building. In general U<0.15 along with 1.0 windows is usually 'enough', and with attention to thermal bridging and airtightness will get your a passivehouse. But if you make a very long thin building, rather than a compact rectangular one U-values need to be significantly better to get the same W/m2/yr.

The other aspect of 'enough' is what are you targetting? Passivehouse 15 kWh/m2.yr or the LETI/AECB 50kWh/m2.yr? Anything in that range is a justifiable target IMHO.

If you do your PHPP sums you should get a pretty good answer for heat load.
In general I would say that U=0.13 for the walls is fine. It's probably OK for the roof too.
I have 100mm PUR on some walls (plus 65mm of fibreglass in the cavity) (U=0.15) (and the EWI walls vary from 0.14 to 0.16) and that (with a lot of airtightness work, U=0.72 windows and U=0.12 ceiling and U=0.16 skeilings) makes for a _very_ comfortable building even though the floor has not been insulated yet. That's a pretty-much optimum-shaped rectangular building.

how much is enough insulation

CJT — Sat, 22 Jul 2023 12:14:33 +0100

Posted By: wookeyHow much is enough depends on the shape of the building. In general U<0.15 along with 1.0 windows is usually 'enough', and with attention to thermal bridging and airtightness will get your a passivehouse. But if you make a very long thin building, rather than a compact rectangular one U-values need to be significantly better to get the same W/m2/yr.

The other aspect of 'enough' is what are you targetting? Passivehouse 15 kWh/m2.yr or the LETI/AECB 50kWh/m2.yr? Anything in that range is a justifiable target IMHO.

If you do your PHPP sums you should get a pretty good answer for heat load.
In general I would say that U=0.13 for the walls is fine. It's probably OK for the roof too.
I have 100mm PUR on some walls (plus 65mm of fibreglass in the cavity) (U=0.15) (and the EWI walls vary from 0.14 to 0.16) and that (with a lot of airtightness work, U=0.72 windows and U=0.12 ceiling and U=0.16 skeilings) makes for a _very_ comfortable building even though the floor has not been insulated yet. That's a pretty-much optimum-shaped rectangular building.

Thank you, that's what i think i am looking for a bit of reassurance that i am in the right area. I could possibly add more IWI to the roof but dont really want to lose more on the walls inside. I have a quote for all the doors and windows Of Â£16k for double glazed fitted at 1.4. Then another for 0.79 triple glazed (not fitted) at Â£26k !!!! Decisions !! Â£28k for solar, Battery and ASHP. Its not cheap trying to do the right thing. /Users/christhompson/Desktop/Screenshot 2023-07-22 at 12.01.36.png

how much is enough insulation

revor — Sat, 22 Jul 2023 16:31:46 +0100

Posted By: CJTÂ£28k for solar, Battery and ASHP.

That sounds a lot what is the spec?

how much is enough insulation

CJT — Sun, 23 Jul 2023 09:25:14 +0100

Posted By: revor
Posted By: CJTÂ£28k for solar, Battery and ASHP.

That sounds a lot what is the spec?

5.27kW 13 405W ja solar panels with Solis 5kW inverter.
Tesla 13.5 kW Powerwall.
Vailant aerotherm 7 kW ASHP with tank etc.

There does seem quite a mark up on the parts when I have researched it. I dont think I want a Powerwall, Probably a Givenergy system.

how much is enough insulation

cjard — Fri, 28 Jul 2023 10:13:49 +0100

In your passivhaus, what will you use the ASHP for? ;)

how much is enough insulation

revor — Fri, 28 Jul 2023 17:17:38 +0100

Posted By: CJTThere does seem quite a mark up on the parts when I have researched it. I dont think I want a Powerwall, Probably a Givenergy system.

Guess the Powerwall is a big part of the cost of the PV probably as much as or more than the rest of it. Most make of batteries you can get via wholesalers but the Powerwall being only available through registered installers puts a fixed price on it.

how much is enough insulation

CJT — Wed, 02 Aug 2023 14:59:27 +0100

Posted By: cjardIn your passivhaus, what will you use the ASHP for? ;)

It isn't my intention to build a passive house i am just trying to get it as comfortable as possible within a reasonable budget. i see a heat pump as my only realistic option for heat and hot water.

how much is enough insulation

djh — Wed, 02 Aug 2023 17:20:57 +0100

Posted By: CJTi see a heat pump as my only realistic option for heat and hot water.

You do seem to be building something close to a passivhaus though. So a heat pump is certainly a good option. I'd have thought 7 kW may be a bit big. What heat loss calculations have you done and what are your hot water plans? Also what overheating calculations have you done?

What software has been used for the calculations? I'd recommend running everything through PHPP since it is supposed to be pretty accurate. It is for our house.

With a 5 kW solar system, one choice for hot water is a simple solar diverter and a dual immersion cylinder or thermal store. One immersion is driven from the solar diverter and will provide all your hot water for most of the year. The other immersion is driven from the mains and is used to fill in when the solar isn't enough. That's the system we have and it works well. The advantages are a very low capital cost and low ongoing maintenance costs. If you do have a heat pump you can substitute that for the second immersion.

In our house I haven't yet been able to justify a heat pump, given the capital costs and maintenance costs involved. We just use direct electric heating when it is required.

edit: just to say I apologize if you've already posted some of this information elsewhere. I didn't check, sorry.

how much is enough insulation

tony — Wed, 02 Aug 2023 20:00:57 +0100

The additional cost of insulation is small compared to paying heating bills.

By far the best, easiest and cheapest time to add insulation is during construction.

I would rather pay once for insulation and not pay heating bills.

Heat pump is a good option, if it is costing thousands I would take 30% of the budget for it and spend that on additional insulation.

HVHR is essential and produces a healthy clean and fresh low cost environment that is worth every penny.

I agree that comfort is important and as well as nice air quality I like slow temperature swings, days/weeks rather than hours >> high thermal inertia being a good thing.

Watch out for overheating, that leads to discomfort, a building physics model will predict overheating days.

how much is enough insulation

CJT — Thu, 03 Aug 2023 18:05:20 +0100

Posted By: djhYou do seem to be building something close to a passivhaus though. So a heat pump is certainly a good option. I'd have thought 7 kW may be a bit big. What heat loss calculations have you done and what are your hot water plans? Also what overheating calculations have you done?

What software has been used for the calculations? I'd recommend running everything through PHPP since it is supposed to be pretty accurate. It is for our house.

I will guiltily say i haven't done any ! I have just looked at the PHPP 240 euros if i am looking at the right thing ? I maybe underestimated somewhat what's involved here !
My hot water plans were the heat pump and heating same via UFH. I had considered the immersion and solar but as yet undecided. I will go back and look at the PHPP.

how much is enough insulation

CJT — Thu, 03 Aug 2023 18:07:16 +0100

Posted By: tonyThe additional cost of insulation is small compared to paying heating bills.

By far the best, easiest and cheapest time to add insulation is during construction.

I would rather pay once for insulation and not pay heating bills.

Heat pump is a good option, if it is costing thousands I would take 30% of the budget for it and spend that on additional insulation.

HVHR is essential and produces a healthy clean and fresh low cost environment that is worth every penny.

I agree that comfort is important and as well as nice air quality I like slow temperature swings, days/weeks rather than hours >> high thermal inertia being a good thing.

Watch out for overheating, that leads to discomfort, a building physics model will predict overheating days.

Hvmr is going in i like the idea.i do need however need to do some heating/over heating calcs

how much is enough insulation

djh — Thu, 03 Aug 2023 20:26:31 +0100

Posted By: CJTI will guiltily say i haven't done any ! I have just looked at the PHPP 240 euros if i am looking at the right thing ? I maybe underestimated somewhat what's involved here !

Hmm, who's doing the SAP calcs? PHPP 10 apparently costs Â£170+VAT from AECB so 240 â‚¬ seems expensive. The main issue is the data entry though; there's quite a lot of it and it's not always immediately apparent what's the right way to input it, but it is important to get the details right. I think the best way is to pay a trained person to build the PHPP model. I know somebody else on here has built their own model in it though, so he may have a different opinion.

But having a good model is well worth the cost since you can optimise insulation and windows etc and save much more that way.

how much is enough insulation

CJT — Sat, 05 Aug 2023 16:33:01 +0100

Posted By: djhHmm, who's doing the SAP calcs?

Sorry i should have said that i am getting a company to do the Saps,

how much is enough insulation

gustyturbine — Mon, 14 Aug 2023 13:43:01 +0100

Posted By: CJT
Posted By: djhYou do seem to be building something close to a passivhaus though. So a heat pump is certainly a good option. I'd have thought 7 kW may be a bit big. What heat loss calculations have you done and what are your hot water plans? Also what overheating calculations have you done?

What software has been used for the calculations? I'd recommend running everything through PHPP since it is supposed to be pretty accurate. It is for our house.

I will guiltily say i haven't done any ! I have just looked at the PHPP 240 euros if i am looking at the right thing ? I maybe underestimated somewhat what's involved here !
My hot water plans were the heat pump and heating same via UFH. I had considered the immersion and solar but as yet undecided. I will go back and look at the PHPP.

My GSHP also does my DHW. I REALLY regret this as my GSHP does still consume a great deal of power in warmer months. I wish I'd fitted PV or solar thermal. During my next build I want to build so no ASHP is needed and use PV immersions or a small HP and reduce running times. I'm also fitting MVHR, 3g, PV.

how much is enough insulation

Jeff B — Mon, 14 Aug 2023 14:56:51 +0100

I wish I'd fitted PV or solar thermal.

Sorry about that GustyTurbine. Having made plenty of mistakes with other decisions, that's the two things I don't regret fitting. The old solar thermal system rumbles on year on year, practically maintenance free and provides free DHW for practically all of mid-May to mid- September.

We got the PV system back in 2011and so are on the maximum tariff (it was part of my pension plan!). With hindsight I think a PV/immersion heater set up might have been better than solar thermal as the latter adds another layer of complexity. I also don't think we make the most of the PV generated power for our own use - I'm sure we export far more than we use but that was the whole point of the tariff I guess. Can't afford a battery storage system sadly!