SIPS v ICF - is Phase shift really a factor?

[Muellar]

Hello

 

I've progressed a house design using ICF, but got concerned at all the detailing so that various things could be installed - from boxed/hidden blinds to fixing of heavy items - and this made me consider SIPS as an alternative.

 

My gut feeling that having density/mass in a build was a good thermal buffer and then reading through various items on BuildHub I found out about decrement and then UBAKUS so I inserted various build profiles to see what the results came out based on a base SIPS option i've seen and then adding 45mm of cork to the outside and finally an ICF build up I like.

 

The benefit of SIPS over ICF now looks to be on the increase I'd get on the internal floor area, with a fixed external allowance, as well as ease of future fixings for what looks to be a marginal benefit due to the difference between the increased phase shift that ICF gives when I look at the temperature difference on the inside surface.

 

Have I got this roughly right or is there a better way to look at this? I have included screenshots of the output from the software for the 3 main scenarios i've considered.

 

[JohnMo]

Decrement decay is real. The other issue is noise transfer. SIPs are quite noise transparent, ICF aren't.

 

Are you comparing similar U Values?

[SteamyTea]

Taking those modelled phase shifts if 7.2, 10.3 and 12.5 hours only really apply on the 2 days a year when each hours of daylight, or hours of darkness, coincide with the phase shift.

The other times the building is cooling or heating.

Did you just model a wall?

The two biggest influences are the glazing area/orientation and the uncontrolled ventilation rates.

A thermally inefficient floor can have an impact as well.

The footprint area to perimetry ratio makes a difference to.

 

Basically once out of the tropics, daylight hours plays a larger and larger harder game the greater the latitude.

 

The UK also has a strange climate, not easy to model reliably as we can have warm nights in the autumn and winter (last week was over 13°C), but quite cold in the spring. Much of this is to do with the sea surface temperature around the UK. It is this relatively high winter SST that makes the UK cloudy.

 

 

Edited yesterday at 17:41 by SteamyTea

[Alan Ambrose]

I never understood this either - is it better to have a 12-hour delay (so the phase shift partially cancels out the temperature driver) or as long a delay as possible (so the inside is as unaffected by the temperature fluctuation as possible)?

[Kelvin]

It’s better to reduce the extent of the glazing. However we bought the plot for the view and full height windows are nice feature in my opinion. Most of our south elevation is glass so the temperature in those rooms varies a lot more and more quickly. The temperature in the other rooms tends to be a lot more stable and consistent. As always  it’s a compromise. 

[saveasteading]

12 hours ago, Kelvin said:

Most of our south elevation is glass 

Because I've been looking at garage doors, I've come across several external rollers for windows. They are not as expensive as I had assumed considering they are outdoors and motorised. I can vouch for how effective these are in Mediterranean weather, keeping sun out in summer and heat in, in winter. 

[-rick-]

9 minutes ago, saveasteading said:

Because I've been looking at garage doors, I've come across several external rollers for windows. They are not as expensive as I had assumed considering they are oitdoors and motorised. I can vouch for how effective these are in Mediterranean weather, keeping sun out in summer and heat in, in winter. 

 

Just had a quick google and first hit with displayed prices suprised me. Combination insulated shutter with fly screen, automatic operation, coming in at less than half the price of pure fly screens I've looked at before. Feel like I've misunderstood or misremembered something.

[SteamyTea]

23 minutes ago, saveasteading said:

I can vouch for how effective these are in Mediterranean weather, keeping sun out in summer and heat in, in winter. 

Well the sun out is because the windows are small, the winter heat leaking out is because they are usually single glazed.

I don't know what it is about the British and the fixation with large windows.

[-rick-]

18 minutes ago, SteamyTea said:

Well the sun out is because the windows are small, the winter heat leaking out is because they are usually single glazed.

I don't know what it is about the British and the fixation with large windows.

 

Now show a modern equivalent mediteranian design. It will have large windows too (though also plenty of shading/overhangs most likely).

 

Old houses has small windows because glass couldn't be manufactured in large sizes. Once large glazing panels became viable people everywhere wanted to use it with varying levels of solar gain mitigation, from brute force carbon intensive mechanical forms to passive approaches.

[SteamyTea]

11 minutes ago, -rick- said:

Now show a modern equivalent mediteranian design. It will have large windows too (though also plenty of shading/overhangs most likely).

Like this one

 

[Nickfromwales]

11 hours ago, SteamyTea said:

I don't know what it is about the British and the fixation with large windows.

In the med you can sit outside and enjoy the views, in the uk you’d get wet and cold doing so, ergo ‘we’ choose portals to view the outdoors / scenery and small windows don’t lend themselves very well to this pursuit.

 

Solar reflective glazing works very well, and only needs buying once / is zero maintenance.
 

Buying heat to offset the reduction in winter solar gain is not worth the argument, in a well insulated, cheap to run dwelling anyways, so afaic fill your boots.

[Muellar]

@JohnMo - I got the U values on the SIPS with cork to be similar to the ICF build up I'm considering so the comparison was as equal as it could be on a U value basis so I could see the difference in decrement values. I did wonder about SIPS and noise but have seen a load of examples of the SIP i'm interested in being built both in city centres and on exposed remote sites (similar to ours) and was told they are quiet. You've got me wondering now.....

[saveasteading]

12 hours ago, -rick- said:

Now show a modern equivalent mediteranian design. 

Your wish is my command.

 

Being a nerd I stopped to look at this small development with finished and in progress together. I thought some of you might like to see both.

Mostly small windows with shutters. One bigger opening, also with shutter.

 

Of course if there is a wonderful view then that would affect the design, but if kept rectangular, the blind can still work.

 

My puritanical streak on this is that some people expect to walk around in T shirts all year. We already have the technology of jumpers  and opening windows.

And really, how often does a UK house suffer from overheating?

 

 

 

[Muellar]

@SteamyTea - as we've got an exposed site and building in Northern Ireland the desire is for a quiet energy efficient home. ICF attracted me but then recently I was shown homes that are similar built using SIPS, my concern with SIPS was that they'd fluctuate too much with the external temps due to lack of mass/density. Reading other threads on Buildhub led me to the UBAKUS site. In turn that led me to taking the standard SIPS build-up I was given and adding cork EWI to see how it would improve the U value to be similar to the ICF and what the resultant decrement was. I was happy with the ICF results I had and to answer your question I guess I am after a 'model wall' based on the ICF characteristics.

 

All other factors I'm good with - glazing/floor/orientation etc. 

[sgt_woulds]

1 hour ago, saveasteading said:

 

And really, how often does a UK house suffer from overheating?

 

 

 

 

 

 

In most houses built since the 70's, enough times that it is leading to excess deaths in the elderly.  

 

Heat mortality monitoring report, England: 2024 - GOV.UK

 

Even amongst the younger population, the lack of sleep caused by an overheated house in a nation where the majority of people cannot properly ventilate overnight (due to the threat of some scrote breaking in) is leading to inflamation and circulatory stress.  At a minimum this leads to lower productivity during the day, and long-term will reduce healthy life expectancy.

 

There have been various studies that show that excess heat increases the incidence of depression and angst in teenagers, etc, etc, etc. 

 

Heatwaves Linked to Rising Depression and Anxiety in Teenagers

 

Heat stress will only increase in the coming years and I'd preffer to see grants for shade solutions and decrement delay rather than subsidised Air-con.

 

Discounts for families to keep warm in winter and cool in summer - GOV.UK     - so short sighted!

 

 

Anyway, back to the OP question.

 

For the love of god don't go with SIPs.  Using SIPs is the single biggest mistake I've made in my build!  Nevever mind the heat - essentialy I've built a giant drum, and no amount of high density stick on insulation can stop the noise transfers throughout the structure.  That means internal noise (like my son playing with marbles upstairs) and external noise (I live near Luton, so aeroplane and traffic noise) is always 'felt', even when you can't hear it.

 

I have 60mm of directly rendered woodfibre externaly, on 150mm of PUR SIPs, with 25mm woodfibre flex inside, battens, resiliant bars, plasterboard.  Heat transfer through the walls is not too bad, but most of my new SIPs walls are North and East facing so not really exposed to the sun.  

 

72m2 SIPs flat roof is the killer though.  60mm of woodfibre over this has not been enough to keep the internal temperatures comfortable.  I'm now looking for reflective paint I can apply to the EPDM.

 

In winter it is easy enough to keep warm.  We invented clothing many thousands of years ago, and survived 1 1/2  iceages without central heating.  Keeping cool is much harder, so really, given the pace of climate change, decrement delay is far more important than u-value in the grand scheme of things. 

 

 

 

If you are considering ICF, why not look at CobBauge too?   

 

 

 

 

Edited 8 hours ago by sgt_woulds

[ProDave]

Have you looked at timber frame, with Wood fibre EWI as I have, the phase shift is about 13 hours, similar to your ICF figure.

 

It is certainly provided a low energy and comfortable building.

[saveasteading]

52 minutes ago, sgt_woulds said:

  I'm now looking for reflective paint I can apply to the EPDM.

This is top of my head reaction as I dont know your roof product in detail... and given read back.

I'm assuming that absorbed heat from direct sunlight is the issue, rather than outside temperatures.

A reflective surface would help hugely, but it gets dirty if flattish and looks poor if raked.

Might it be more effective to fit an additional roof covering... a sunshade effectively.  If this was raised by 50mm or so then it would radiate some heat,   have an air gap and also allow air cooling through draughts. 

The outer material could be metal cladding (uninsulated), board and any waterproofing, or tiles.

If the roof was flat then paving slabs on pads.

 

This would reduce the absorbed heat massively. 

 

 

[Kelvin]

I’ve been in a few SIPs built houses (all Heb Homes) and also noticed they weren’t very sound proof from outside noises. I’d already decided not to use SIPs for other reasons but it added to my list of why I wouldn’t use it. The space frame we built is very quiet however it does suffer a bit from vibration but only at the French doors in that if they are shut quite hard you can feel the vibration very slightly upstairs. 

[Muellar]

38 minutes ago, Kelvin said:

I’ve been in a few SIPs built houses (all Heb Homes) and also noticed they weren’t very sound proof from outside noises. I’d already decided not to use SIPs for other reasons but it added to my list of why I wouldn’t use it. The space frame we built is very quiet however it does suffer a bit from vibration but only at the French doors in that if they are shut quite hard you can feel the vibration very slightly upstairs. 

Thanks for that feedback Kelvin. Our site whilst not in a built up area or on a flight path is exposed so we will get a lot of wind noise, plus livestock in the fields and crows.... those crows make a heck of a racket. Noise is a key factor for us and is one of the reasons ICF appealed, ain't much going through c 155mm of concrete and triple glazed units. 

 

It's starting to look like we'd be best putting up with the longer construction time ICF has and getting the detailing right early given we hope for this to be a home we'd live in for 20+ years.

[Muellar]

 

1 hour ago, ProDave said:

Have you looked at timber frame, with Wood fibre EWI as I have, the phase shift is about 13 hours, similar to your ICF figure.

 

It is certainly provided a low energy and comfortable building.

This wasn't on my list as i'd discounted TF some time back purely due to a number i'd visited that didn't give me a feeling of warmth. I guess it's maybe due to them having been thrown up and if done proprely they'd be great but the dye was cast and i've yet to experience a TF home that gives me the feeling I seek. Sounds like you've got it right though, typical eh.

[JohnMo]

We have an ICF house, (wood crete, not polystyrene), it's silent, the only noise comes through the triple glazed windows.

[sgt_woulds]

44 minutes ago, saveasteading said:

This is top of my head reaction as I dont know your roof product in detail... and given read back.

I'm assuming that absorbed heat from direct sunlight is the issue, rather than outside temperatures.

A reflective surface would help hugely, but it gets dirty if flattish and looks poor if raked.

Might it be more effective to fit an additional roof covering... a sunshade effectively.  If this was raised by 50mm or so then it would radiate some heat,   have an air gap and also allow air cooling through draughts. 

The outer material could be metal cladding (uninsulated), board and any waterproofing, or tiles.

If the roof was flat then paving slabs on pads.

 

This would reduce the absorbed heat massively. 

 

 

 

With the woodfibre over the SIPs needing to breath, we already have a hybrid warm roof.  Construction from inside is:

 

plasterboard on resiliant bars, 25mm woodfibre flex , VVCL, 270mm SIPs / 60mm wood fibre (wet process highest density) / breather membrane / 80mm ventilated zone / 18mm OSB deck / EPDM.

 

The detritus stuck to the eaves ventilation slits attest to the strength of airflow accross the roof.  Unfortunately with the roof span and margins for snow loading, there is no spare capacity to add PV panels, sedum, etc to provide any more buffering, so paint it will have to be

[Kelvin]

1 hour ago, Muellar said:

Thanks for that feedback Kelvin. Our site whilst not in a built up area or on a flight path is exposed so we will get a lot of wind noise, plus livestock in the fields and crows.... those crows make a heck of a racket. Noise is a key factor for us and is one of the reasons ICF appealed, ain't much going through c 155mm of concrete and triple glazed units. 

 

It's starting to look like we'd be best putting up with the longer construction time ICF has and getting the detailing right early given we hope for this to be a home we'd live in for 20+ years.

If I as building again I’d quite likely go ICF I think. 

[JohnMo]

7 minutes ago, Kelvin said:

If I as building again I’d quite likely go ICF I think. 

ICF is easy, and I quite enjoyed the process. Other options worth consideration, block work with external insulation or Larson Truss with dense infill insulation. Both should give thermal bridge free build and great protection from heat and cold.

[Kelvin]

2 minutes ago, JohnMo said:

ICF is easy, and I quite enjoyed the process. Other options worth consideration, block work with external insulation or Larson Truss with dense infill insulation. Both should give thermal bridge free build and great protection from heat and cold.

Ours is a little like a Larsen truss. Full fill and deep walls.