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Lintels With Different Thermal Efficiency? (Block Built House)


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#1 JamieM

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Posted 21 March 2016 - 10:21 AM

Lintels with different thermal efficiency? (Block built house)

Hi - a quick question on lintels (I have also posted a similar question about sills but wanted to keep the 2 topics separate). I don’t know much about lintels but just curious if there is anything I should be looking for in terms of energy efficiency?

Also - We have a few lintels in our plans that are greater than 2 metres including 3 corner lintels (2 in a sun room and one corner of the house). Our architect has recommended keystone lintels. Just curious if anyone has any experience of using them and or their competitors?

I am aware we’ll have to get the SE calculations for the larger openings.

bit of background on our build.
-Block built
-150mm cavity full PIR board insulation
- Windows – u value roughly less than 0.8u
- Fairly well insulated house.

I’m based in NI – Antrim/Ballymena

Thanks

Jamie

#2 declan52

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Posted 21 March 2016 - 11:41 AM

I have a corner window in mine and it's the actual post that is the major risk of a cold bridge. You have to make sure it's wrapped before the window guy measures up or the L shaped cladding he uses mightn't fit. Aerogel is the best to use but the dearest.
There are lintels that keystone do that are better thermally and I think shell looked into them, not sure if she used them or not though. Have used keystone lintels for years, probably the most widely available here in NI.

#3 PeterW

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Posted 21 March 2016 - 11:44 AM

Keystone are very good - they are also very well priced.

even the thermally broken lintels have a bridge in them - if you looking at block / block then you can remove the bridge by using two independent lintels, one for each skin

#4 DeeJunFan

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Posted 21 March 2016 - 11:53 AM

I was thinking of a corner window but removed it for this reason.

My brother is just finishing a build and he included 3 of them. There are fairly large posts and the steel bridges all the way from the internal skin to the external so not something i would be keen on.

he has used the same build up as you 150mm full fill and all i can say is you will need to be on top of your builders everyday. i did a walk round of my brothers house when the block work was finished and i saw some really bad fitting. at least 3 boards were back to front (and thats what i could see from door and window reveals). And at least 50% of the boards were more than 5mm from the internal blockwork.

I would go with separate concrete lintels for all openings were possible and try and do whatever you can to minimise bridging around the corners. But you will have to accept that they will always be a thermally weak spot and any moisture will be attracted to them.

#5 declan52

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Posted 21 March 2016 - 11:54 AM

Is there any reason you are going for a lintel rather than a concrete head. Can't use concrete for the corner windows but I used it on all the rest of my openings. Will be cheaper than a lintel but not as easy lifted. My biggest opening is 3.8m and I used a pre stressed concrete head for it. Couldn't get a machine in to lift it so used a pulley block and scaffolding to get it into place. That was a fun day.
I agree with dee about the insulation if its not done right it will be a waste of money. Have you priced beads in the cavity. Probably cheaper and will give a better u value in the real world, Pir better on paper.

Edited by declan52, 21 March 2016 - 11:56 AM.


#6 JamieM

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Posted 21 March 2016 - 01:10 PM

DeeJunFan - Do you remember what sort of full fill PIR your brother used – we are thinking of using Xtratherm’s cavitytherm product and its really obvious which side goes to the outside (although I know mistakes can always happen). It’s on my partners land and she does intend to walk around the site every evening to check the likes of this. I like the idea of using a lintel for each block the way yourself and PeterW suggested.

Declan - there is no reason I am going for a lintel rather than a concrete head. I will have to look into the concrete heads, would there not be the possibility of more cold bridging with them? The beads would be cheaper to install I would imagine though then I would need a bigger cavity (around 225mm-250mm) to match the PIR (on paper). Also, thanks for the advice on the corner post. That is something we will have to look out for. Good to know these things!

#7 tonyshouse

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Posted 21 March 2016 - 01:46 PM

In well nsulated house best to have seperate lintels on the inside and outside skins as this will mitigate the vast majority of the horrendous thermal bridging that normal lintels bring.

#8 DeeJunFan

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Posted 21 March 2016 - 02:00 PM

My brother used Xtratherm, but the builder also bought some kingspan full fill (which a completely different produce EPS not PIR)

and they managed to install some of each the wrong way round.

They must have taken a saw to it and cut off the joints to do it so I can't see what they were thinking.

#9 kev106

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Posted 21 March 2016 - 06:51 PM

I would go with concrete lintels where possible. With the correct detailing there will be no cold bridging at all. On the corner windows you will just have to accept that it will be a weak point thermally in the house. Keystone will do your structural calcs for the corner lintels if you send them the plans.
In regards to the use of xtratherm, I'm a bricklayer and I'd strongly advise you to consider a slightly bigger cavity and use pumped beads. As much as you try to keep an eye on things (brickie's) there will be gaps behind the boards, mortar bridging the cavity (especially with full fill products) and gaps horizontally and vertically between the boards.


#10 JamieM

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Posted 21 March 2016 - 10:21 PM

Has anyone on here changed the insulation from pir to the beads and upped their cavity (say from 150mm to 225mm). Just curious how much extra work would be involved? Ie wider foundations, closing off the cavity etc.

Just had a look at sliders blog. Looks like he managed it ok.

I'm also not sure if bc would have anything to say. They might not be too keen but I suppose it's never know till I asked them.



#11 joe90

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Posted 21 March 2016 - 10:27 PM

I plan a 300mm cavity with either rockwall batts ( like tonyshouse) or pumped beads, BC said it should not be a problem for them.

#12 jsharris

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Posted 21 March 2016 - 10:33 PM

I like the idea of pumped bonded beads. It removes a lot of the uncertainty about workmanship that you get with bats, and is more likely to give an insulation layer than doesn't have gaps in it that reduce the effectiveness. EPS bonded beads are also good for walls exposed to hard weather, as they are unaffected by moisture and still allow anything that gets through the outer skin to drain down without penetrating the insulation.

#13 Woodgnome

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Posted 22 March 2016 - 12:32 AM

View Postjoe90, on 21 March 2016 - 10:27 PM, said:

I plan a 300mm cavity with either rockwall batts ( like tonyshouse) or pumped beads, BC said it should not be a problem for them.

I looked at full fill pumped beads, but couldn't find anyone to do it!

Edited by Woodgnome, 22 March 2016 - 12:33 AM.


#14 declan52

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Posted 22 March 2016 - 07:15 AM

View PostJamieM, on 21 March 2016 - 10:21 PM, said:

Has anyone on here changed the insulation from pir to the beads and upped their cavity (say from 150mm to 225mm). Just curious how much extra work would be involved? Ie wider foundations, closing off the cavity etc.

Just had a look at sliders blog. Looks like he managed it ok.

I'm also not sure if bc would have anything to say. They might not be too keen but I suppose it's never know till I asked them.
Cost wise to go an extra 75mm wider cavity you will have an extra block on the outside of your founds. The amount of sand and cement extra won't be that much then whatever your brickie is charging you per block.
You will have longer wall ties which will be a bit extra. Need wider asbestolux then to close the cavity. All in all not much more and probably still cheaper than pir insulation in the cavity.

#15 DeeJunFan

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Posted 22 March 2016 - 08:03 AM

View Postdeclan52, on 22 March 2016 - 07:15 AM, said:

Cost wise to go an extra 75mm wider cavity you will have an extra block on the outside of your founds. The amount of sand and cement extra won't be that much then whatever your brickie is charging you per block.
You will have longer wall ties which will be a bit extra. Need wider asbestolux then to close the cavity. All in all not much more and probably still cheaper than pir insulation in the cavity.

talking about the asbestolux i could only get 150mm or 300 mm tried all the merchants around but no-one kept any 9 inch stuff so anything over a 150mm cavity would be buying the bigger boards.

#16 JamieM

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Posted 29 March 2016 - 11:35 AM

Thanks for all the advice guys. After reading through, I think we are going to go for separate (one for the inner and one for the outer leaf) concrete heads for the majority of the openings. Would anyone have a technical cross section of the best way to install them avoiding thermal bridging?

#17 tonyshouse

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Posted 29 March 2016 - 11:57 AM

Good decision!

There is a sectional sketch on my website or a full size model here

Edited by tonyshouse, 29 March 2016 - 11:58 AM.


#18 JamieM

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Posted 29 March 2016 - 12:47 PM

Cheers Tony will have a look later when I get a free minute.

#19 JamieM

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Posted 31 March 2016 - 09:33 AM

Only getting round to looking at this now, is below the sketch you are referring to Tony? You also mention a full size model, is there a link missing?

Could I ask a quick simple question(as I can't quick see it from the sketch) . When 2 concrete heads are used, how is between the 2 concrete heads closed off? Is it just using rigid PIR?

Thanks

Jamie

#20 declan52

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Posted 31 March 2016 - 11:07 AM

Cut a bit of 100mm/ 50mm pir and wedge it in the gap. When the beads get blown in it will fill any holes. Once the windows go they will cover the most of the gap. Any more will be covered in when you plaster it. Might need a bit of plasterboard bonded to the head just depends on the width of your cavity and the width of your windows.