Cold bridging around windows

fatty pang

I thought I would take this question over into the 'thinking mans' section of C&P to see if anybody has any observations on the issue.

http://www.boards.ie/vbulletin/showpost.php?p=98525479&postcount=13

fatty pang

90 odd views and no comment so…. errr… presumably nobody is using a 100 masonry inner leaf without a closer block.
If it’s just the Passive House crowd doing it then I’ll not worry – THERM is the Godhead

fatty pang

90 odd views and no comment so…. errr… presumably nobody is using a 100 masonry inner leaf without a closer block.
If it’s just the Passive House crowd doing it then I’ll not worry – THERM is the Godhead

ht9zni1gs28crp

The problem with this site is people who have experience do not bother posting helpful insights and tips anymore. Some of the begrudgery stuff you get back makes it not worth your while.

fatty pang

Each to their own. Personally I find the parish is much more agreeable these days.

rampantbunny

Similar detail used on my build insofar as plywood used to close cavity. However, in addition, I have an aluminium angle on the inside face of the external block, to which the plywood is fixed i.e. plywood itself is anchored to outside leaf.
Window straps are fixed to internal leaf blockwork (100mm on edge), through the ply closer. Plywood acts as a sort of strap across the cavity itself.

I'm probably not the 'thinking man' you are looking for here, but still I 'think' the above offers a better anchor solution. I've not read any of the literature you referenced in your linked post, but the above is my 2c seeing as your post isn't getting much in the way of response.

Please don't ask me what my engineer thought (or didn't).

Metric Tensor

Edit: Big long post

I had a big long post put up for the sake of a good chat about the issue but on reflection I deleted it because I was too worried about someone taking it from this site and presenting it as fact elsewhere or using it to justify some hair-brained scheme.

It's terrible really that you have to be afraid of such things but that the type of character does sometimes float through these parts!!!

Happy to discuss it by pm with any of you who did see it!!!

sydthebeat

i think people are slow to post on this because of the charter..... Issues relating to the specification of structural components is prohibited

BryanF

sydthebeat wrote: »

i think people are slow to post on this because of the charter..... Issues relating to the specification of structural components is prohibited

True

miller_63 wrote: »

The problem with this site is people who have experience do not bother posting helpful insights and tips anymore. Some of the begrudgery stuff you get back makes it not worth your while.

True, but is there a point where knowledge/experience is worth paying for?

Metric Tensor

I think that was miller_63's point - you go to a lot of hassle to write a long post explaining the correct way to do something and then because it's more expensive than the way they were told by some chancer at the pub you get a response filled with contempt rather than thanks!

I don't envy your job modding BryanF!

Metric Tensor

Sorry - I keep doing that. It's just a habit using the "Quick Reply" option.

fatty pang

sydthebeat wrote: »

i think people are slow to post on this because of the charter..... Issues relating to the specification of structural components is prohibited

As no structural components are being “specified” I believe the following is suitable for discussion if only because I believe a discussion is necessary and I can’t think where else it is going to happen.
The elephant in the room is that an open cavity of various widths with 100mm masonry walls is a very common detail.
Authoritative guidance (BS 8213-4: 2016) states “Fixings should be sized to securely penetrate at least 40 mm for windows and 50 mm for doors into brick, block, concrete or masonry, or 25 mm into timber framing unless equivalent demonstrable provision can be made by other means.”

If 'demonstrable provision' can’t be provided how can anybody stand over such a fixings ?
The only relevant guidance offered in this country is TGD-A which somewhat oddly provides guidance on the structural safety of external wall cladding whilst excluding windows (sic);
1.3.2 - Wall cladding presents a hazard if it becomes detached from the building. For the purposes of this section, cladding is deemed to include glazed curtain walling but not windows.

1.3.4 - Wall cladding should be capable of safely sustaining and transmitting to the supporting structure of the building all the actions which are liable to act on it.

1.3.5- Wall cladding should be securely fixed to and supported by the supporting structure of the building.

Loading
1.3.8 -Wind actions on the wall cladding should be derived from I.S. EN 1991-1-4. Due consideration should be given to local increases in wind suction arising from funnelling of wind through gaps between buildings.

Fixings
1.3.12 - The selection of fixings for securing cladding should be determined from consideration of the proven performance of the fixing and the risks associated with the particular application

1.3.13 - For design purposes, the strength of a fixing should be derived from tests using materials representative of the base material of the structure into which the fixing is to be anchored. Account should also be taken of any inherent weaknesses in the base material of the structure which may affect the design strength and durability of the fixing, e.g. cracks due to shrinkage or flexure, or voids in masonry construction. (emphasis added)

A window, particularly an assembly of windows or large sliding doors, is subject to the same loads as ‘cladding’ and certainly presents a ‘hazard’ if it should become detached.

sydthebeat

can you break this down for us FP... are you questioning the distance from the frame to the fixing...
ie a 50mm frame, a 150 cavity and 100 inner leaf would mean approx 125mm from the edge of the frame to the fixing...

or

are you questioning the depth the fixing is inserted into the substructure?
thats seems to be what is specified above ie 50mm or more into a block wall.... which is no problem.

also, cant the windows be fixed to the external leaf if necessary?

im not a structural engineer, so im just asking these questions

rampantbunny

sydthebeat wrote: »

can you break this down for us FP... are you questioning the distance from the frame to the fixing...
ie a 50mm frame, a 150 cavity and 100 inner leaf would mean approx 125mm from the edge of the frame to the fixing...

or

are you questioning the depth the fixing is inserted into the substructure?
thats seems to be what is specified above ie 50mm or more into a block wall.... which is no problem.

also, cant the windows be fixed to the external leaf if necessary?

im not a structural engineer, so im just asking these questions

I think FP is questioning the distance of the anchor from the face of the block. Take a 5mm fixing for example, inserted into the middle of a 100mm block. This fixing is now 47.5mm from both the front and rear face of the block. Pressure exerted inwards due to external force on the window pushes against this 47.5mm of block. Similarly, pressure outwards.

sydthebeat

my reading of " “Fixings should be sized to securely penetrate at least 40 mm for windows and 50 mm for doors into brick, block, concrete or masonry, or 25 mm into timber framing unless equivalent demonstrable provision can be made by other means.”

is

“Fixings should be sized to securely penetrate at least 40 mm for windows and 50 mm for doors into brick, block, concrete or masonry, or 25 mm into timber framing unless equivalent demonstrable provision can be made by other means.”

so their talking about the depth of the fixing into the substructure??

sydthebeat

my reading of " “Fixings should be sized to securely penetrate at least 40 mm for windows and 50 mm for doors into brick, block, concrete or masonry, or 25 mm into timber framing unless equivalent demonstrable provision can be made by other means.”

is

“Fixings should be sized to securely penetrate at least 40 mm for windows and 50 mm for doors into brick, block, concrete or masonry, or 25 mm into timber framing unless equivalent demonstrable provision can be made by other means.”

so their talking about the depth of the fixing into the substructure??

rampantbunny

That's what I would read from that excerpt Syd, but from FPs linked post:

With the block on edge there is a 100mm exposed face to accept the fixing. I’m not aware of any fixing into masonry that has a recommended minimum edge distance of <50mm – which will, ipso facto, occur in this instance.

fatty pang

rampantbunny wrote: »

I think FP is questioning the distance of the anchor from the face of the block. Take a 5mm fixing for example, inserted into the middle of a 100mm block. This fixing is now 47.5mm from both the front and rear face of the block. Pressure exerted inwards due to external force on the window pushes against this 47.5mm of block. Similarly, pressure outwards.

‘Edge distance’ of the fixing is indeed the salient point.
Many typical wall constructions feature a 100mm block on edge







An 8mm frame fixer requires a minimum edge distance of 50mm for a concrete block - see page 6
http://www.fischer.co.uk/PortalData/10/Resources/support/sales-documents/documents/3.Frame_Fixings___Stand_Off_Installation_No_Bleed_18.12.12sml.pdf

The lightweight blocks as shown on edge (page 7) in this IAB certificate require 100-150mm edge distance. http://www.ribaproductselector.com/Docs/3/23663/external/COL223663.pdf

The block on edge doesn't work.

fatty pang

sydthebeat wrote: »

also, cant the windows be fixed to the external leaf if necessary?

Typically the outer leaf is also 100mm block (won’t work on a checked brick reveal) so the same problem of edge distance arises and running a strap through the line of the DPC isn’t great practice

im not a structural engineer, so im just asking these questions

Same here.