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I've just spotted an advertisement for this company in a magazine, which piqued my interest. They seem a newish venture and offer a shell build service only. The screwpiles seem to be optional. They quote a u-value of 0.16 using SIPs - is that good? Any thoughts?

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Ihave built a copule of industrial workshops with steel --,but for normal house the only reason ican see for using portal frame is if going grand designs with all sorts of cantilevered flying lounges .

 

sips have enough strength for a house ,so why the steel?

a long way for a short cut

yes value seems possible if sips totally envelope steel frame --

look at industrial portal buildings using composite panels if that the way you want go they get same sort of values but with finish as well..

 

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Thanks @scottishjohn. I'm still pondering on which build system to use, and since I'm building a bungalow I can't really see what advantage a steel frame would have over the timber alternatives, especially SIPs, since I'm hoping to put rooms in the roof space. At the moment it's all about research, including reading this excellent forum!

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rooms in roof space then sips will give you more space than anything else if ridge height is a problem.

but you could build with ICF and have a sips roof 

so many choices 

I know cos i,m going through same things myself

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SIP's as roof panels aren't a good idea, IMHO.  They inevitably need internal rafters between the skins, as SIP panels are strong in compression, as walls, but nowhere near as stiff in bending, and the internal rafters tend to create repeating thermal bridges.  Also, SIP insulation tends to have a pretty low decrement delay, so for room-in-roof designs there will be a tendency for those rooms to overheat more rapidly when the sun's shining on the roof, and conversely cool more quickly during a cold night.

 

I'm not sure the importance of decrement delay is getting across well here, but it is key to making a living space comfortable; more important than the overall insulation and airtightness spec in many ways.

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20 minutes ago, scottishjohn said:

rooms in roof space then sips will give you more space than anything else if ridge height is a problem.

 

..? A SIP roof to meet BRegs insulation standard will be exactly the same thickness as one with full fill PIR. Chances are both will need internal insulation or insulated plasterboard. 

 

In terms of heat loss, a SIP roof with timber spines will lose more than one built with I-Joists of the same thickness. 

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1 minute ago, PeterW said:

 

..? A SIP roof to meet BRegs insulation standard will be exactly the same thickness as one with full fill PIR. Chances are both will need internal insulation or insulated plasterboard. 

 

In terms of heat loss, a SIP roof with timber spines will lose more than one built with I-Joists of the same thickness. 

 

We had this discussion a few years ago on Ebuild, before its demise, and I remember calculating the losses through the repeating thermal bridges from the required internal rafters on 190mm deep roofing SIPs, the thickest then available, and it was pretty grim.   They were also a lot more expensive than other options.

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8 minutes ago, PeterW said:

 

..? A SIP roof to meet BRegs insulation standard will be exactly the same thickness as one with full fill PIR. Chances are both will need internal insulation or insulated plasterboard. 

 

In terms of heat loss, a SIP roof with timber spines will lose more than one built with I-Joists of the same thickness. 

why would you use timber splines? use proper insulated splines  and  if  required have a gable to gable support at half distance from ridge to top of walls 

and yes you will need a services void so batton out inside and use foam backed plaster board if you need to 

I doubt you will if you go for a 175 or200mm sips panel --you can even get 225mm sips easily now

Edited by scottishjohn

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7 minutes ago, scottishjohn said:

why would you use timber splines? use proper insulated splines  and  if  required have a gable to gable support at half distance from ridge to top of walls 

and yes you will need a services void so batton out inside and use foam backed plaster board if you need to 

I doubt you will if you go for a 175 or200mm sips panel --you can even get 225mm sips easily now

 

How are you going to get a roofing SIP to take the bending loads without internal rafters between the skins?  I asked all the SIP manufacturers about this, as we were originally going for a SIP build for our house (I spent over 6 months working with a SIP build company, and we went through loads of options), and none made roofing panels that didn't have internal rafters.  Not surprising, as the shear strength of the foam core is pretty low. 

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29 minutes ago, JSHarris said:

SIP's as roof panels aren't a good idea, IMHO.  They inevitably need internal rafters between the skins, as SIP panels are strong in compression, as walls, but nowhere near as stiff in bending, and the internal rafters tend to create repeating thermal bridges.  Also, SIP insulation tends to have a pretty low decrement delay, so for room-in-roof designs there will be a tendency for those rooms to overheat more rapidly when the sun's shining on the roof, and conversely cool more quickly during a cold night.

 

I'm not sure the importance of decrement delay is getting across well here, but it is key to making a living space comfortable; more important than the overall insulation and airtightness spec in many ways.

you keep going on about this 

I assume the people who make super cold storage facilities know what they are doing as heat loss costs them money --not one of them use blown fibres all use pir insulation so it must be better --the bean counters would soon work out which way costs them less to keep temp at -40c when outside can be +30c.

so you are perfectly entitled to your opinion ,but I will go with  what the big money people use,where initial cost is secondary to running costs .

If you gonna make your house super insulated and air tight the top rooms are always going to be hot in summer as heat rises.

 

 

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So a 225 SIP will still need a supporting beam at its midpoint as it cannot span a 5m span unsupported. The purlin for that would be dependent on the span but would be fairly large. 

 

I can’t find any supplier that states you can use an insulated spline in a roof - most say solid timber or the use of “reinforced SIPs” which are effectively 6x2 encased in OSB and injected insulation. The thermal bridges are still there and the challenges of installing 150-200kg panels remains. 

 

 

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1 minute ago, JSHarris said:

 

How are you going to get a roofing SIP to take the bending loads without internal rafters between the skins?  I asked all the SIP manufacturers about this, as we were originally going for a SIP build for our house (I spent over 6 months working with a SIP build company, and we went through loads of options), and none made roofing panels that didn't have internal rafters.  Not surprising, as the shear strength of the foam core is pretty low. 

just to be simple look at kingspan tek house -video  and you will see hows its done,

uk.video.search.yahoo.com/search/video?fr=mcafee&p=u-tube+and+kingspan+tek#id=3&vid=533dcaebfbac7e80df66273d603efb87&action=click

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10 minutes ago, PeterW said:

So a 225 SIP will still need a supporting beam at its midpoint as it cannot span a 5m span unsupported. The purlin for that would be dependent on the span but would be fairly large. 

 

I can’t find any supplier that states you can use an insulated spline in a roof - most say solid timber or the use of “reinforced SIPs” which are effectively 6x2 encased in OSB and injected insulation. The thermal bridges are still there and the challenges of installing 150-200kg panels remains. 

 

 

It will still be less intrusive than 300-400mm roof trusses.which you then have to fill with insulation .

hire of a telehandler for a day is hardly a big deal when whole roof goes on in few hours along with waterproof membrane all in same day .

I agree if you are having full flat ceilings upstairs with an attic /junk space .then go with trusses ,still doubt it will be cheaper or simpler ,but where planning says 1.5 stories only then space is important

Edited by scottishjohn

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15 minutes ago, scottishjohn said:

just to be simple look at kingspan tek house -video  and you will see hows its done,

uk.video.search.yahoo.com/search/video?fr=mcafee&p=u-tube+and+kingspan+tek#id=3&vid=533dcaebfbac7e80df66273d603efb87&action=click

 

It still doesn’t meet either structural or building regs ..! The absolute maximum a 172mm SIP panel can span is 2.8m and it’s U Value doesn’t meet the regs for England or Scotland as it’s 0.16w/mK Whole house in Scotland is now 0.11 for roof, with a limiting fabric factor of 0.15. 

 

8 minutes ago, scottishjohn said:

will still be less intrusive than 300-400mm roof trusses.which you then have to fill with insulation .

hire of a telehandler for a day is hardly a big deal when whole roof goes on in few hours along with waterproof membrane all in same day

 

You don’t need 300mm roof trusses. A 240mm steico can span 5.8m at 400mm centres. If that is full fill with 190mm rockwool and then 50mm PIR between followed by 50mm over, the roof easily hits the 0.11 required. It’s 290mm deep, has a long decrement delay and will also have a decent sound absorbtion. 

 

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45 minutes ago, scottishjohn said:

you keep going on about this 

I assume the people who make super cold storage facilities know what they are doing as heat loss costs them money --not one of them use blown fibres all use pir insulation so it must be better --the bean counters would soon work out which way costs them less to keep temp at -40c when outside can be +30c.

so you are perfectly entitled to your opinion ,but I will go with  what the big money people use,where initial cost is secondary to running costs .

If you gonna make your house super insulated and air tight the top rooms are always going to be hot in summer as heat rises.

 

 

 

Sorry, but have you looked at the impact of decrement delay, as it seems you're focussed on one aspect of performance, thermal conductivity?

 

For a comfortable, well-insulated and airtight house decrement delay is very important.  Cold storage facilities aren't designed for comfort, and decrement delay isn't at all important, but thermal conductivity and airtightness are.  House are not cold storage facilities though; if they were then they could be designed and built the same way.

 

FWIW, our upstairs rooms don't get hot at all, and they are room in roof, with vaulted ceilings, and that's because I made sure that we used a high decrement delay roof design.

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sorry it still don,t, make sense passage of hot or cold  is the same .

 think you are forgetting is the foam is never seeing the direct heat from sun as the roof slates , have a 4" gap with the cross battoning and a self perpetuating air flow between tiles and sips  from the soffits to the ridge .unless what you are saying is you are quite happy for heat to leak out of the roof ,

as for kingspan not meeting building code --maybe not if all you used was the sips alone ,but you know as well as i that you would batton inside for services then foam plaster board which will make it comply.

are basically saying you are making a cold roof structure and only the last layer of pur is doing the work and the blown fibres are just to make a slow moving air space .

I fully understand that air is a very poor conductor of heat .

are you also saying that doing it this way there is little need for mvhr

looks a lot more expensive + time consuming  to build .

I will bring this up with the architect --but if it twice as costly --i,ll open the windows in summer

Edited by scottishjohn

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Back on Ecosteel, from the illustrations the steelwork appears to completely bridge the SIPs, which slot into the beam. I'd have thought this almost completely cancels out the insulation and also a condensation risk. The steels look like they are then covered internally with something like OSB, which would not do well with any condensation. Odd why they don't wrap the frame externally as is standard for sandwich panels.

 

Insulated panels external to a frame (perhaps steel) I think still deserves a look, but this particular design seems a bit suspect to me.

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8 hours ago, kxi said:

Back on Ecosteel, from the illustrations the steelwork appears to completely bridge the SIPs, which slot into the beam. I'd have thought this almost completely cancels out the insulation and also a condensation risk. The steels look like they are then covered internally with something like OSB, which would not do well with any condensation. Odd why they don't wrap the frame externally as is standard for sandwich panels.

 

Insulated panels external to a frame (perhaps steel) I think still deserves a look, but this particular design seems a bit suspect to me.

If using steel frame total wrap with the insulation is only solution ,thats what modern portal frame buildings  do with the composite cladding panels attached to outside of structure,unless you are going for the INDUSTRIAL look then you would need to strap out whole interior the same  to start with  for a house

 

Edited by scottishjohn

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9 hours ago, JSHarris said:

FWIW, our upstairs rooms don't get hot at all, and they are room in roof, with vaulted ceilings, and that's because I made sure that we used a high decrement delay roof design.

 

Our upstairs rooms don't overheat and some have vaulted ceilings and we don't have high decrement delay insulation. As I have said before whether you need to use high decrement delay materials is dependent on a lot of factors. From what you have described before, you created a sheltered site which means that the use of high decrement delay materials is very important in your build construction. I'm confident that if I had used a more dense insulation I wouldn't have noticed any beneficial effects.

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9 hours ago, scottishjohn said:

sorry it still don,t, make sense passage of hot or cold  is the same .

 think you are forgetting is the foam is never seeing the direct heat from sun as the roof slates , have a 2" gap with the cross battoning and a self perpetuating air flow between tiles and sips  from the soffits to the ridge .unless what you are saying is you are quite happy for heat to leak out of the roof ,

as for kingspan not meeting building code --maybe not if all you used was the sips alone ,but you know as well as i that you would batton inside for services then foam plaster board which will make it comply.

are basically saying you are making a cold roof structure and only the last layer of pur is doing the work and the blown fibres are just to make a slow moving air space .

I fully understand that air is a very poor conductor of heat .

are you also saying that doing it this way there is little need for mvhr

looks a lot more expensive + time consuming  to build .

I will bring this up with the architect --but if it twice as costly --i,ll open the windows in summer

 

 

You're still missing the decrement delay issue.  If you take two flat structures, with an identical thermal conductivity (U value), but where one has a decrement delay that is, say twice as long as the other, then heat will take twice as long to travel from one face to the other of the high decrement delay structure.  The U value is immaterial in this specific case, what is significant is the dynamic effect of the rate of change of heat transfer, when conditions change, as they do during the day as the sun's position varies, cloud cover changes or at night when radiative loss changes with cloud cover. 

 

Roof slates have virtually no effect at all, as they heat up to a high temperature in the sun and re-radiate from their rear surface - that's simple physics.  That means that the surface under the roof covering still gets very hot.  I have a couple of DS18B20 sensors under our PV panels (which are in-roof, with a ~50mm air space behind them) and despite the fact that the PV panels are removing around 18% of the energy and turning it into electricity (which is another good argument for using PV, it helps keep the roof cooler in sunny weather) I still see temperatures on the top surface of our sarking of over 40 deg C pretty regularly.  That air space is well ventilated, too, with vents at the top and bottom to help reduce the temperature build up and ensure that the sarking boards stay nice and dry.

 

This has nothing to do with MVHR, it's just simple physics as applied to structures and heat flow through them, by a mix of conduction and radiation in the main, although air flow does result in some external convective effects, hence the impact of wind speed, which results in accelerated convection from any exposed surface.

 

As mentioned before, when the air temperature outside is higher than you want the air temperature inside, opening windows will just make the house warmer.  Opening the windows at night, using a night purge system as is fairly common in hotter climates. does work well, though, when the night time temperature is low enough.  This takes advantage of the long thermal time constant of well-designed house, by extracting heat from the interior during the cooler night time, so lowering the internal temperature, and the house then takes a long time time to warm up the next day, because the structure has a long decrement delay. 

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6 minutes ago, PeterStarck said:

Our upstairs rooms don't overheat and some have vaulted ceilings and we don't have high decrement delay insulation. As I have said before whether you need to use high decrement delay materials is dependent on a lot of factors. From what you have described before, you created a sheltered site which means that the use of high decrement delay materials is very important in your build construction. I'm confident that if I had used a more dense insulation I wouldn't have noticed any beneficial effects.

 

The specs for icynene shows that it does have a fairly high decrement delay for foam insulation, as far as I can see from the limited data available.  It's certainly got a decrement delay that's maybe double that of PIR, just based on the published lambda and an assumed value for specific heat capacity based on similar spray foam materials.

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 will  be looking into this some more --but still not convinced for same old reason --

If cold store uses pir when they got to keep using fuel to keep to -40c  -then it has to be best insulation EG stoppage of the passge of heat from one layer to next  at all times

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18 minutes ago, scottishjohn said:

 will  be looking into this some more --but still not convinced for same old reason --

If cold store uses pir when they got to keep using fuel to keep to -40c  -then it has to be best insulation EG stoppage of the passge of heat from one layer to next  at all times

 

 

It's not about thermal conductivity on it's own, it's about decrement delay, which is the combination of thermal resistance and heat capacity of the structure.  There's loads of stuff on the web explaining this, but in essence the higher the decrement delay of a structure the slower heat will travel through it for a given set of conditions.  Time is the key here, and thermal conductivity (or it's inverse, thermal resistance) doesn't have a time component.

 

We live in a climate where the outside surface temperature of buildings often varies over a wide range within a 24 hour period, yet we like our homes to not vary much in temperature at all.  This means that the time it takes heat to travel through a structure has a significant influence on the temperature inside the building, and hence the comfort level.  Building structures that have a long decrement delay provides a way of delaying the transmission of heat during times when one side is hotter than the other, which works both ways.  It slows down the rate of heat transfer during times when the sun is shining on the outside, and also slows down the rate of heat transfer when the temperature outside suddenly drops, say a cold night after a warm day. 

 

The consequence of this is that the temperature inside remains more stable than it otherwise would.  Key to this is that the periods when the outside surfaces of a building are too hot or too cold for comfort are relatively short; a few hours or so each day.  If we can increase the decrement delay to a time longer than the typical time that the outside surface is too hot or too cold, then we can reduce the impact this has on internal temperature variations, which in turn makes the building more comfortable.

 

There are other factors that contribute to this too, as the relatively high specific heat capacity of the plasterboard lining, plus the substantial heat capacity of the all the interior components, floor slab, etc, will absorb heat from the interior as it warms up, so slowing the rate of change of room air temperature and also release heat to the room air as that cools down. 

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2 minutes ago, JSHarris said:

 

 

It's not about thermal conductivity on it's own, it's about decrement delay, which is the combination of thermal resistance and heat capacity of the structure.  There's loads of stuff on the web explaining this, but in essence the higher the decrement delay of a structure the slower heat will travel through it for a given set of conditions.  Time is the key here, and thermal conductivity (or it's inverse, thermal resistance) doesn't have a time component.

 

We live in a climate where the outside surface temperature of buildings often varies over a wide range within a 24 hour period, yet we like our homes to not vary much in temperature at all.  This means that the time it takes heat to travel through a structure has a significant influence on the temperature inside the building, and hence the comfort level.  Building structures that have a long decrement delay provides a way of delaying the transmission of heat during times when one side is hotter than the other, which works both ways.  It slows down the rate of heat transfer during times when the sun is shining on the outside, and also slows down the rate of heat transfer when the temperature outside suddenly drops, say a cold night after a warm day. 

 

The consequence of this is that the temperature inside remains more stable than it otherwise would.  Key to this is that the periods when the outside surfaces of a building are too hot or too cold for comfort are relatively short; a few hours or so each day.  If we can increase the decrement delay to a time longer than the typical time that the outside surface is too hot or too cold, then we can reduce the impact this has on internal temperature variations, which in turn makes the building more comfortable.

 

There are other factors that contribute to this too, as the relatively high specific heat capacity of the plasterboard lining, plus the substantial heat capacity of the all the interior components, floor slab, etc, will absorb heat from the interior as it warms up, so slowing the rate of change of room air temperature and also release heat to the room air as that cools down. 

so basically we should build conrete bunker with insulation on the outside ?

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9 minutes ago, scottishjohn said:

so basically we should build conrete bunker with insulation on the outside ?

 

 

ICF, or block construction with EWI is one way to get a long decrement delay, but there are others, and concrete is far from being the only way to get a reasonably high decrement delay.  Finding information on the decrement delay of different build options isn't easy at all, but the shortest decrement delay insulation that's commonly used is probably PIR/PUR.  EPS and Icynene have between 1.5 and 2 times the decrement delay of PIR, dense rockwool, wood fibre and blown cellulose have between 2 and 3 times the decrement delay of PIR (all assuming the same overall thermal conductivity value).

 

To a certain extent, insulation materials with a higher lambda tend to also have a longer decrement delay, as well as insulation materials with a higher heat capacity also having a higher decrement delay.  It's the combination of the two that determines the overall figure, and, most importantly, it isn't just the insulation that is important in determining this, it's the entire build up of the structure, be it a wall or roof.

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