Extra insulation

[jpinthehouse]

Hi

I am going to stick build my timber frame 140mm, was going upgrade to fully fill the studs with 140 celotex with 50mm over the top rather than just 120mm in between.

Upgrade slab insulation from 100mm celotex to 150mm

Roof upgrade from 200mm in between and 20mm underneath to 200mm and 50mm underneath

I have a block external skin.

Is it worth the extra cost.

Thanks

John

 

[Onoff]

You only pay for insulation ONCE which is a bit of a motto on here. 

 

You pay for fuel in whatever form FOREVER.

 

Yes it's worth it imo.

[PeterW]

Have a look at the cost benefit of 30mm over vs 50mm. You may find for the .01 it improves the uValue of the walls it has such an extended payback period it will neither offset the cost of the extra material or the longer fixings required over 25 years. You're better looking at the air tightness and controlling the heat loss there as it's a larger impact. 

[MikeSharp01]

By definition it will be worth the extra cost eventually but you would need to do the sums a bit to find out just how much energy you save each year and then work out the payback time if its a pure financial calculation. Many here though see it as important to tread a bit lightly on the planet so insulation is often to passive house standards and as such you try to see the saving over the very long term. Key thing though is to factor in the probable rises in energy costs over the next 10 years, some predict large rises and that makes the insulation even more valuable.I think that the spreadsheet @JSHarriscreated would do the sums for you as it can take a what if sort of approach. You can find a link here:

[Jeremy Harris]

There are a couple of points here. 

 

First there is the cost benefit one, which is hard to pin down, because you may find that the relatively modest cost of additional insulation fitted during the build may reap a greater return through life that it appears from simple calculations.  The effect of local conditions can make a marked difference to heat loss and gain, so it often isn't as straightforward as it seems to work out the benefit.  We encountered just this problem, by accidentally creating an area where our build is that is warmer than the surrounding area all year around, gets a lot more solar gain that anticipated and loses a lot less heat than expected.

 

Secondly there is the comfort factor.  Having more insulation of a type that increases the decrement delay factor makes a big difference to the way the house feels.  Houses with a high internal heat capacity and good insulation, plus good airtightness and decent heat recovery ventilation, tend to have a longer thermal time constant, so they heat up more slowly in very hot weather and cool down more slowly in very cold weather.  This tends to improve comfort levels a lot.

 

This latter point is not always well-understood, but there is a good article here that explains, in broad terms, how decrement delay affects comfort levels: http://www.greenspec.co.uk/building-design/decrement-delay/

 

Simply changing from a low decrement delay factor insulation product, like all forms of foam insulation, to one with an equivalent, or better, thermal performance, but with a higher decrement delay, can make a significant difference to the comfort level inside the house, both in winter and summer. 

[A_L]

FWIW IMHO,

 

1) Stud upgrade, worth it, even if small additional costs elsewhere.

2) Slab upgrade, worth it, even more if UFH.

3) Roof upgrade, probably not.

 

[ProDave]

I would echo what Jeremy has said.  PIR /PUR types as you are proposing have a relatively low decrement delay, meaning the house will cool down quicker when it gets cold out side (very basic version)  I am using Earthwool Frametherm 35 to insulate in between the studs (195mm studs in my case) and 100mm thick wood fibre board as external wall insulation. Both have a longer decrement delay (though you need more of them to get the same U value)

 

Frametherm or similar is a lot easier to fit into a stud wall (that's what it's designed for) Stiff enough to push in and stay without slump even in a sloping roof, but compressible enough that you don't need to be perfect with your cutting. Fitting solid slabs into a timber frame you need to be precise otherwise you leave an air gap, or be prepared to fill any gap with expanding foam.

 

I hit a brick wall at the early stages of planning my build. As soon as I mentioned to a standard timber frame kit builder that I wanted to upgrade and add extra insulation, they refused to quote. I ended up getting a more experienced architectural technician to detail what I wanted, and a local firm of builders to build the frame to that spec and erect it.

[MikeSharp01]

1 hour ago, JSHarris said:

This latter point is not always well-understood, but there is a good article here that explains, in broad terms, how decrement delay affects comfort levels: http://www.greenspec.co.uk/building-design/decrement-delay/

Brilliant reference Jeremy, just worked out our decrement delay at 8.99 hours using the ARUP calculator with FRAMETHEREM (as @ProDave has used and we are proposing) and 11.39 hours using Cellulose Infill (as you @JSHarris have). Might need to improve ours a bit! Also found this reference for loads of materials and their properties, bit of a Kaye and Laby, but full of useful material values to pop into the ARUP calculator - did not find blown cellulose yet, so used the cellulose infill values. Also this from the Federation of European Polyurethane associations on PU foam.

 

Here is pic of calculation for you @jpinthehouse

 

Edited September 16, 2017 by MikeSharp01
Typo

[Oz07]

How can people be sure of above inflation cost rises for fuel. In the medium term there are loads of poorly insulated houses still around which have no chance of being replaced or upgraded to "a" epc rating. 

 

Both the big parties have talked about energy price caps so I would bet against over inflation fuel rises. Anything further than 20 years and most self builders could be downsizing!

[Crofter]

1 hour ago, Oz07 said:

How can people be sure of above inflation cost rises for fuel. In the medium term there are loads of poorly insulated houses still around which have no chance of being replaced or upgraded to "a" epc rating. 

 

Both the big parties have talked about energy price caps so I would bet against over inflation fuel rises. Anything further than 20 years and most self builders could be downsizing!

 

If you think our politicians can control the wholesale price of energy, then you have a lot more faith in them than I do.

[bassanclan]

I vaguely remember a thread about insulation "the sweet spot" but I can't find it, maybe on ebuild?

[Jeremy Harris]

Energy prices for domestic consumers have been increasing for decades.  The rate of change varies, and is impacted by world events, like oil shortages resulting from conflicts, but overall the price just steadily increases in the long term, no matter what governments do.  This, slightly dated, blog entry has a reasonably good indication of how prices varied between 1998 and 2012: http://www.yougen.co.uk/blog-entry/2353/What+is+the+real+inflation+rate+for+energy'3F+/

 

There were some peaks and troughs, but overall the trend has always been upwards, and is likely to remain so.  For comparison, my pay over the same period increased at a far lower rate than the average energy price increase.  Not sure that's that significant, but I would guess that it's not untypical for energy prices to increase faster than pay, in the longer term.

[Jeremy Harris]

2 minutes ago, bassanclan said:

I vaguely remember a thread about insulation "the sweet spot" but I can't find it, maybe on ebuild?

 

I'm not sure there is a universal sweet spot.  A big house can probably get away with less insulation than a small house, but will reap a greater benefit from reduced ventilation heat loss, as volume versus surface area plays a large part in things.  In general, the smaller the house the more important insulation level is.

[Crofter]

2 hours ago, JSHarris said:

 

I'm not sure there is a universal sweet spot.  A big house can probably get away with less insulation than a small house, but will reap a greater benefit from reduced ventilation heat loss, as volume versus surface area plays a large part in things.  In general, the smaller the house the more important insulation level is.

OTOH, the smaller the house, the smaller the heating requirements in absolute terms. Sometimes I think we forget this.

[CC45]

DO NOT put 140mm celotex into a 140mm frame.  I did this - never again.  The celotex sheets vary in thickness - a surprising number were more than 140mm, this causes BIG issues when you come to putting battens on. I've spent hours, in fact weeks putting spacers behind the battens to lift then off the frame - all because of the celotex.  I would urge you to use 120mm.  The celotex web site has a u-value calc on it - 20mm less wont make much difference but it WILL save your sanity.  I was given this advice before I ordered our celotex and like an idiot I ignored it.  I dont want you to make the same mistake I did.

Edited September 16, 2017 by CC45
Clarity

[PeterW]

I'd go a slightly different route on the Celotex. Get a price on 60mm and 75mm and do two layers - slightly cheaper on material normally but it's easier to handle and cut in two layers. You will need to factor in the labour but it's not a difficult job and you will find you get a better fit. 

[jpinthehouse]

Hi

Thanks for all the replies, am definitely going to upgrade

John

[Roundtuit]

With regards to decrement delay, I can see that those of you with cladding as the rain screen will have to give more thought to insulation types, but surely the OP's block outer skin and obligatory 50mm cavity will have a significant beneficial effect on internal temperature stability?

[jpinthehouse]

Hi

Looking at celotex prices, I am now considering knauf frame fill, 140mm with celotex over the top,the values are not much different and with good airtight membrane fitting, will the difference be noticeable

Thanks

John

[Declan52]

No and in the real world will end up better. It takes a lot of time and work to cut sheets of insulation perfect or you end up with gaps that need filled. Frame fill is easy to cut and springs out and doesn't budge. Me and a few others went down this route. 

Just make sure that you get the higher density version as it's better u values. 

[jpinthehouse]

Hi Declan

I was looking at frame therm roll 32 w/mk 0.032, as opposed to 120mm celotex w/mk 0.022.

My building regulations have been passed so do I need to resubmit or just talk to become

Thanks

John

[Oz07]

BCO usually agree during build providing your as built SAP will still stack up

[Declan52]

49 minutes ago, jpinthehouse said:

Hi Declan

I was looking at frame therm roll 32 w/mk 0.032, as opposed to 120mm celotex w/mk 0.022.

My building regulations have been passed so do I need to resubmit or just talk to become

Thanks

John

Whatever you add on underneath will be the important bit to get you a pass. The BC guy doesn't really care what you use as long as when he does your as built sap it gives a pass. 

Have you used Jeremy's calculator to mess about with different widths to see what will get you a pass and what the budget will stretch to.

[PeterW]

My sloping loft roof is Frametherm 40 at 190mm plus 25mm Kingspan over the top. BCO said they would accept VCL as the Celotex taped however its been much easier to use plastic sheet to create the VCL and then Kingspan over the top. If I can find some decent tape we will also Aluminium tape over the Kingspan joints for twice the air tightness ..!!