Extension blockwork shell insulation

[masamune]

I have shown my structural plans for a rear extension to two builders and they both asked the exact same question. Which was "why has the engineer used a solid wall with insulation on the outside and not a cavity wall?"

Pic attached



A third builder said this is fine and used in modern construction. Go figure now...

I am no expert in walls and insulation, the only standard wall structure I am familiar with is the cavity sandwich of 100mm block/100mm insulation/100mm wall.

For some reason, be it a lot of glazing or something else, my engineer decided to build the wall as in the drawing attached.

Are there any disadvantages to this external wall e.g how do I fix things on the outside and how sturdy is this formation?

Any thoughts, advice most welcome I approach him with the builder's question.

 

[vinn]

You dont appear to be having much luck with your "builders" and "designers" & "engineers"?

The drawing you posted is a scan from a well known google site.

The drawing is inaccurate.

 

[^woody^]

Any thoughts, advice most welcome

Ask whoever drew the plans. My mind reading machine is in for service.

 

[masamune]

You dont appear to be having much luck with your "builders" and "designers" & "engineers"?

The drawing you posted is a scan from a well known google site.

The drawing is inaccurate.

You only hear about the ones who haven't done a good job

Can you explain what you mean by inaccurate? i.e missing information?

I received this together with a structural plan and structural calculations (i.e timber beams specs, blockwork stress, general load bearing lintels etc). Most builders said they were happy to quote from this but the engineer said we need the building regs drawings for further detail.

Perhaps I should post this last bit under building regs forum.

 

[masamune]

Ask whoever drew the plans. My mind reading machine is in for service.

Fail to understand the unfriendly tone, is this question unreasonable?

I simply asked if this is common blockwork for extensions following comments from two builders.

 

[^woody^]

Fail to understand the unfriendly tone, is this question unreasonable?

Unfriendly? That was exactly how I used to talk to my only friend.

The crux is, how are we to know why someone might design something in a particular way. There is no other information as to why something might have been done, and there may well be several reasons why that has been done.

How's that, matey. Shall we do lunch now?

 

[masamune]

Unfriendly? That was exactly how I used to talk to my only friend.

The crux is, how are we to know why someone might design something in a particular way. There is no other information as to why something might have been done, and there may well be several reasons why that has been done.

How's that, matey. Shall we do lunch now?

Lunch sounds good ...perhaps I misread your post.

To rephrase my question, has anyone come across this type of shell as opposed to cavity?

Just to educate myself before approaching the engineer.

 

[tomfe]

Yes, ewi is a good way to build, normally with a 190/215mm aerated block work as you've got, though I would personally want a fibolite.
If the builder has not done ewi before you want a professional in as the detail while not hard will make all the difference. You may also want to swap to a thicker layer of eps than k5 as k5 has had problems with delamination.

If you want to see some ewi just go to the local council estate there are bound to be some solid wall properties which have had eco money spent on them. Thought they most likely will be pebble dashed and have horrid plastic covers on services.

 

[masamune]

Thanks tomfe, this is really useful to know. A quick list of questions below,

1. Sounds as a non-invasive method used to insulate retrospectively? i.e older properties?
2. Is it thermally equivalent to cavity or better?
3. Is there a particular reason you prefer fibolite from other blocks? Does this have to be decided by the engineer or the builder?

Noted the comment about K5 delamination, I will drop an email to the engineer.

 

[tomfe]

EWI relatively new in the UK but been used in Europe on new builds for 'ages'. It gained a lot of publicity after the green deal was launched then with ECO for improving solid wall properties.
A cavity can be what ever u-value you want it to be you just need to make it wider, this of course has problems, if you look at the Denby Dale house it has 300mm cavity.
Thermalite/aerated blocks move a lot and they are a harder to fix into. Though with EWI thermal movement is minimised.
Thermalite 215mm 75mm k5 u-value ~ 0.19
Fibolite 215mm 75mm k5 u-value ~ 0.22

 

[^woody^]

Ewi is a last resort method for the UK climate. I struggle to find a reason why it would be specified for an extension to a property that does not already have it.

 

[wessex101]

As tomfe said the detail shown is popular to build on the continent. It is intended to be quicker and cheaper especially if you use that new fangled narrow joint blockwork. Trouble is we are not familiar with it so that speed and cost saving may not be achieved.

A house was built near me recently using that method and the walls went up incredibly quickly.

 

[masamune]

EWI relatively new in the UK but been used in Europe on new builds for 'ages'. It gained a lot of publicity after the green deal was launched then with ECO for improving solid wall properties.
A cavity can be what ever u-value you want it to be you just need to make it wider, this of course has problems, if you look at the Denby Dale house it has 300mm cavity.
Thermalite/aerated blocks move a lot and they are a harder to fix into. Though with EWI thermal movement is minimised.
Thermalite 215mm 75mm k5 u-value ~ 0.19
Fibolite 215mm 75mm k5 u-value ~ 0.22

The engineer is originally from Europe and had experience there before so that probably explains it.

If I understand correctly from your u-values, Thermalite blocks offer better insulation but are harder to fix?

From what I gather this is a slightly unfamiliar construction design for a number of builders. I wonder if worth discussing an alternative with the engineer, in case there are issues down the line or the builder struggles to deliver a good quality finish on this type of wall.

How would you fix something heavy externally on this wall, would you use deeper bolts to fix it on the blocks behind the insulation?

 

[masamune]

Ewi is a last resort method for the UK climate. I struggle to find a reason why it would be specified for an extension to a property that does not already have it.

This is slightly concerning, although if proved to be a good alternative I'd be happy to go with it provided the builder has experience on EWI.

The problem is that it would limit the builder selection, while some can be good with on a number of other challenging tasks required for the extnesion job.

 

[^woody^]

The engineer is working under your instruction. Tell him that you want a traditional insulated cavity wall that is compliant to any applicable current regulations.

This will attract a premium for any quotes, and yes it will limit choice of builder whilst unnecessarily increasing risk both in construction, longer term, and at sale time.

There is no advantage and no need to build this type of wall.