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Kurt Barlow

Insulation options behind timber cladding

Question

Completed on our house purchase on Thursday. The house is early 80's vintage

Our house, at least the upper floor is not cavity wall. Its 9 inch block work (very light stuff - a bit like a whispa bar). There is then a layer of bitumen type sheet (same as roof felt) and then shiplap boarding mounted on battens. 

Research suggests this isn't as good as cavity wall from a thermal perspective but I can see some advantages as there are no issues with corroded cavity wall ties. 

The boarding will probably need to be replaced in 3-5 years so Id like to improve the insulation. 

Bit wary of using kings span type stuff - Don't want a mini Grenfell

Rockwool tends to get wet 

Aerogel is best performing stuff but prohibitively expensive. 

Other option is foil backed bubble wrap type insulation but not certain as to performance and not sure if I'd want a breathable barrier. 

Thoughts? 

Edited by Kurt Barlow

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Can buy other multiple layer mylar type foils which can be stapled direct to battens - you may be restricted in type of insulation (thickness) due to soffits anyway, still not cheap but probably cheaper than aerogel. As there is a bitumen layer then presumably the build design is for a non-permeable external wall - you can get the films in breathable/non permeable types I think so probably won't need another layer so this method could do both jobs in one with appropriate sealing tape. Will want to make sure proper ventilation behind cladding with suitable stud work arrangement. Improve but don't do overboard I reckon, you are never going to get passivehaus standard so take pragmatic approach. 

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10 hours ago, onlyme said:

Can buy other multiple layer mylar type foils which can be stapled direct to battens - you may be restricted in type of insulation (thickness) due to soffits anyway, still not cheap but probably cheaper than aerogel. As there is a bitumen layer then presumably the build design is for a non-permeable external wall - you can get the films in breathable/non permeable types I think so probably won't need another layer so this method could do both jobs in one with appropriate sealing tape. Will want to make sure proper ventilation behind cladding with suitable stud work arrangement. Improve but don't do overboard I reckon, you are never going to get passivehaus standard so take pragmatic approach. 

Thanks:)

I reckon the gap could accommodate 20-25mm. 

If I use foil I will over lap but not seal with tape so that way moisture can get out. The local style is black timber cladding so I

suspect that will heat up rapidly and dry out any moisture that is there. The timber clad walls face east and west. 

I picked up a job lot of 200mm insulation on ebay so am insulating the loft. I reckon there is enough to double layer to 400mm on top of the 50mm currently in there. Will also double insulate all the pipes and water tanks. 

 

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1 minute ago, Kurt Barlow said:

Thanks:)

I reckon the gap could accommodate 20-25mm. 

If I use foil I will over lap but not seal with tape so that way moisture can get out. The local style is black timber cladding so I

suspect that will heat up rapidly and dry out any moisture that is there. The timber clad walls face east and west. 

I picked up a job lot of 200mm insulation on ebay so am insulating the loft. I reckon there is enough to double layer to 400mm on top of the 50mm currently in there. Will also double insulate all the pipes and water tanks. 

 

Just for clarity, you bought a 1980s house?  o.O

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Just to clarify.  You want external wall insulation?  Can be better than internal wall insulation but not really a DIY job to do properly.  Soffits, window ledges, services, getting a good seal, adhesion, etc,  You'll need to meet building regs if changing over 25% of a surface area (a specific definition of what this is exists) which may require PIR (Celotex type stuff), definitely more than 25mm, to avoid massive thickness or costs (Aerogel).  Internal may be easier, preferably with PIR board, if you can lose a bit of space.  Not sure on the fire status of PIR.  Celotex pulled some products and Grenfell used the wrong stuff.  The  price of PIR (at least at my merchants) has gone crazy due to an alleged (ironic) factory fire (but which was a long time ago).  Ty Mawr offer alternative insulation products to PIR board.  They are lime specialists but their insulation products don't all need to use lime.  Their website also shows some wall build ups.  Bitumen cover is rubbish given it's not breathable.  All that was available back in the day.  Not the case now.  Grants may be available for external wall insulation.  Not sure about not sealing the insulation.  Could create thermal bridging (cold spots), reducing performance and risking internal damp.  Your walls are really single skinned?  No cavity and the breeze block not filled?  Wow!  We call that a "farmer's build" - all he had in the yard at the time!

Edited by Harley

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2 hours ago, Harley said:

Just to clarify.  You want external wall insulation?  Can be better than internal wall insulation but not really a DIY job to do properly.  Soffits, window ledges, services, getting a good seal, adhesion, etc,  You'll need to meet building regs if changing over 25% of a surface area (a specific definition of what this is exists) which may require PIR (Celotex type stuff), definitely more than 25mm, to avoid massive thickness or costs (Aerogel).  Internal may be easier, preferably with PIR board, if you can lose a bit of space.  Not sure on the fire status of PIR.  Celotex pulled some products and Grenfell used the wrong stuff.  The  price of PIR (at least at my merchants) has gone crazy due to an alleged (ironic) factory fire (but which was a long time ago).  Ty Mawr offer alternative insulation products to PIR board.  They are lime specialists but their insulation products don't all need to use lime.  Their website also shows some wall build ups.  Bitumen cover is rubbish given it's not breathable.  All that was available back in the day.  Not the case now.  Grants may be available for external wall insulation.  Not sure about not sealing the insulation.  Could create thermal bridging (cold spots), reducing performance and risking internal damp.  Your walls are really single skinned?  No cavity and the breeze block not filled?  Wow!  We call that a "farmer's build" - all he had in the yard at the time!

Cheers

It would be less than 25% as its only the upper storey and doesn't include the gable end which is an extension built with brick and block. 

More than 25mm means increasing the over hang over the lower storey which Id prefer not to do but would like to increase the insulation if I strip off the timber and replace.

Yep - 9 inch blockwork (they are solid but very airy - like a whisper bar) . I was talking to our neighbour who said the houses are quite warm. The energy company quoted 140 quid a month for  gas and electric based on the previous owners usage. The house has a 1990's boiler and not more than about 50mm of loft insulation*.

As of today thats changed to 450mm of insulation. 

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21 hours ago, Kurt Barlow said:

Completed on our house purchase on Thursday. The house is early 80's vintage

Our house, at least the upper floor is not cavity wall. Its 9 inch block work (very light stuff - a bit like a whispa bar). There is then a layer of bitumen type sheet (same as roof felt) and then shiplap boarding mounted on battens. 

Research suggests this isn't as good as cavity wall from a thermal perspective but I can see some advantages as there are no issues with corroded cavity wall ties. 

The boarding will probably need to be replaced in 3-5 years so Id like to improve the insulation. 

Bit wary of using kings span type stuff - Don't want a mini Grenfell

Rockwool tends to get wet 

Aerogel is best performing stuff but prohibitively expensive. 

Other option is foil backed bubble wrap type insulation but not certain as to performance and not sure if I'd want a breathable barrier. 

Thoughts? 

XPS (extruded polystyrene ) is as good as it gets not that cheap though it`s also closed cell ,it`s not really flammable as it`s self extinguishing 

And if you are thinking of internal as well you can get the same stuff laminated onto plasterboard which i can confirm is amazing 

Edited by Long time lurking

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58 minutes ago, Kurt Barlow said:

Cheers

It would be less than 25% as its only the upper storey and doesn't include the gable end which is an extension built with brick and block. 

More than 25mm means increasing the over hang over the lower storey which Id prefer not to do but would like to increase the insulation if I strip off the timber and replace.

Yep - 9 inch blockwork (they are solid but very airy - like a whisper bar) . I was talking to our neighbour who said the houses are quite warm. The energy company quoted 140 quid a month for  gas and electric based on the previous owners usage. The house has a 1990's boiler and not more than about 50mm of loft insulation*.

As of today thats changed to 450mm of insulation. 

The blocks sound like thermalite blocks ,basically made from fly ash from coal fired power stations and are used for the thermal qualities as the name suggests 

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27 minutes ago, Long time lurking said:

XPS (extruded polystyrene ) is as good as it gets not that cheap though it`s also closed cell ,it`s not really flammable as it`s self extinguishing 

And if you are thinking of internal as well you can get the same stuff laminated onto plasterboard which i can confirm is amazing 

I insulated my first house (Victoria Terrace with a single skin extension) with that stuff. It was a mix of 40mm polyurethane & polystyrene backed plasterboard. That was back in 1996 but I put in 800-900ft2 of the stuff. The days of 12 quid a month gas bills!

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14 minutes ago, Kurt Barlow said:

I insulated my first house (Victoria Terrace with a single skin extension) with that stuff. It was a mix of 40mm polyurethane & polystyrene backed plasterboard. That was back in 1996 but I put in 800-900ft2 of the stuff. The days of 12 quid a month gas bills!

There`s a whole world of difference between extruded and expanded polystyrene i think 1in of the former has the R value of 4in of the later  

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43 minutes ago, Long time lurking said:

XPS (extruded polystyrene ) is as good as it gets not that cheap though it`s also closed cell ,it`s not really flammable as it`s self extinguishing 

And if you are thinking of internal as well you can get the same stuff laminated onto plasterboard which i can confirm is amazing 

Kingspan produce this which has a Class 0 fire rating

https://www.insulationsuperstore.co.uk/product/kingspan-kooltherm-k5-external-wall-insulation-20mm-18m2-pack.html

I could stick in:

20mm of insulation

Breather membrane

20mm batten

19mm shiplap boarding over the top. 

That will bring the upper storey wall flush with the lower storey which appears to be cavity wall. 

 

Just now, Long time lurking said:

There`s a whole world of difference between extruded and expanded polystyrene i think 1in of the former has the R value of 4in of the later  

I got most my supplies from Graham Group. They had run out of polystyrene board which was cheaper so about half was polyurethane (which is better) but the nice chap there charged me the same price. 

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10 minutes ago, Kurt Barlow said:

Kingspan produce this which has a Class 0 fire rating

https://www.insulationsuperstore.co.uk/product/kingspan-kooltherm-k5-external-wall-insulation-20mm-18m2-pack.html

I could stick in:

20mm of insulation

Breather membrane

20mm batten

19mm shiplap boarding over the top. 

That will bring the upper storey wall flush with the lower storey which appears to be cavity wall. 

 

Probably to thick this but it`s well worth checking the shop out you can get some real bargings ,most is over orders or slightly marked 

https://www.ebay.co.uk/i/183698064479?chn=ps&norover=1&mkevt=1&mkrid=710-134428-41853-0&mkcid=2&itemid=183698064479&targetid=594043225830&device=c&mktype=pla&googleloc=1007415&poi=&campaignid=6466403028&mkgroupid=78240852180&rlsatarget=aud-629407025185:pla-594043225830&abcId=1140486&merchantid=113798454&gclid=EAIaIQobChMI6cfG8uHT5AIVV-DtCh2wkg9ZEAYYByABEgIWO_D_BwE

Edit was not the shop i thought it was but it has plenty of Styrofoam which is XPS

Edited by Long time lurking

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34 minutes ago, Long time lurking said:

20-25mm is ideal. Anything thicker and I would have an overhang. 

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1 hour ago, Long time lurking said:

A small over hang can be beneficial ,as it would act like a drip bead ,but  whether it would be pleasing  on the eye is a different matter 

I cant do that because the weatherboard is interlocked into the brickwork at the gable end. 

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On 15/09/2019 at 14:26, Kurt Barlow said:

I reckon the gap could accommodate 20-25mm.

Your later comment suggests you're aware... The air gap behind the boards is important.  Airflow prevents moisture buildup, and capilliary action transference of water.

 

On 15/09/2019 at 22:22, Kurt Barlow said:

I could stick in:

20mm of insulation

Breather membrane

20mm batten

19mm shiplap boarding over the top. 

That will bring the upper storey wall flush with the lower storey which appears to be cavity wall. 

 
Not sure your membrane has any point being breathable, unless the insulation underneath is also breathable?

Presume the 20mm batten will have air in between?

This seems a reasonable proposition - but 20mm isn't a lot of any sort of insulation, even the good stuff.  And £10 a square is eye watering.  But, if it fits into the same space you had before, its probably the simplest solution, and shouldn't be too bad on labour, or too complex if you're diy-ing.

----------------------

Externally insulate the whole thing with, say 100mm of some type of foam - mesh and cement render or timber board the whole house? 

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