Blocklayers- detailing around windows

about2build

Hi guys I've met with a couple of block layers in lieu of starting building in months time....Two options have been presented in relation to the detailing around the windows
1 Use 3 inch L blocks returned toward outer leaf
2 Cut block and turn in toward outer leaf and place some insulation board (1-2 inchs) between outer leaf and this block piece.

The cvavity is 150 mm

The L blocks are expensive as well 1 euro a block which will add up

Thoughts?

BryanF

about2build wrote: »

Hi guys I've met with a couple of block layers in lieu of starting building in months time....Two options have been presented in relation to the detailing around the windows
1 Use 3 inch L blocks returned toward outer leaf
2 Cut block and turn in toward outer leaf and place some insulation board (1-2 inchs) between outer leaf and this block piece.

The cvavity is 150 mm

The L blocks are expensive as well 1 euro a block which will add up

Thoughts?

were these the only options offered?

about2build

Ya Bryan, I'm worried about cold bridging as well, what you think?

BryanF

ye PM sent

sydthebeat

dont cut the blocks, fill the 150 at opes with rigid insulation.
windows etc are fixed by brackets on inner leaf.

fclauson

Suggest you get someone to detail out Ope prior to laying a single block

windows in low energy demand build offer the biggest headache for getting right - and the biggest thermal bridge if you get it wrong

will pm you a name

esox28

fclauson wrote: »

Suggest you get someone to detail out Ope prior to laying a single block

windows in low energy demand build offer the biggest headache for getting right - and the biggest thermal bridge if you get it wrong

will pm you a name

can you pm me please

thank you

fclauson

PM sent

about2build

Thanks guys, syd can you elaborate a bit....what fixes the rigid insulation in place to close the cavity?

Mellor

about2build wrote: »

Thanks guys, syd can you elaborate a bit....what fixes the rigid insulation in place to close the cavity?

THe fact that it has nowhere else to go.

gears

fclauson wrote: »

Suggest you get someone to detail out Ope prior to laying a single block

windows in low energy demand build offer the biggest headache for getting right - and the biggest thermal bridge if you get it wrong

will pm you a name

Any chance of that PM aswell, thanks.

sydthebeat

about2build wrote: »

Thanks guys, syd can you elaborate a bit....what fixes the rigid insulation in place to close the cavity?

its friction fitted between the DPC and the inner leaf.

The fitting of the window frame then abuts it and allows for cavity pumping.

fclauson

gears wrote: »

Any chance of that PM aswell, thanks.

PM sent

braftery

In order to really deal with the openings properly you need to consider the full wall build up .. including internal and external finishes.

For Example:

The use of stone on a building exterior. I have seen 4 different block laying solutions used in different parts of the country .. each with their pros and cons.

Traditionally people have considered making the building water tight as the primary objective and they have compromised all other issues to satisfy this one.

The stonemason job is to make the stone look well and stay on, the block layers job is to put the blocks up true, level and plum.

Do you think they are the best people to solve your buildings cold bridging issues ?

I suggest you sketch a section of the wall as it will look in the finished building ... work out the water tightness, air tightness and cold bridging issues on paper for the full envelope and then give instructions to the block layers.

Or hire someone to give you advice and draw these details for you.

Buying great components is not enough to build a great house .. you need to know how to put them all together too.

scuggels

What about the use of a cavity closer made by xtratherm suits cavity of 150mm? no need for cutting blocks etc

about2build

Thanks guys, it seems no matter what the L block or cutting of blocks is a bit out dated in a low energy build....i'm going to look at the insulated cavity closers tomorrow with a salesman from xtratherm and see what he has to say-what do you think of this option syd/mellor/anyone else but the friction fitted rigid insulation looks a cheaper option.

fclauson

braftery wrote: »

Or hire someone to give you advice and draw these details for you.

Buying great components is not enough to build a great house .. you need to know how to put them all together too.

Good Advice Brian

one component of our house (the porch) has taken
an architect to design
an engineer to specify
an thermal bridge advisor to detail out
a window person add input
a builder to suggest what is practical
and a wife to say what is acceptable

Window and door thresholds are no longer a simple job for "Bodge it and Cludig it" - there is a huge amount of detail to go to get it right

follow the chinese sayong
measure 11 times - cut once

about2build

Thanks guys, i've done that and been told thta an L block is needed for structural reasons but that it will only cover 50mm and that the other 100mm should be filled using a cavity closer. He also recommends keeping the L face back 20mm from the outer leaf so as to facilitate an insulated board to also be fitted...
what ya think guys

sinnerboy

about2build wrote: »

what ya think guys

Sorry to be blunt - but stop talking to blocklayers. Hire an expert to provide detailed drawings and instructions for them to follow.

fclauson

we have a 250mm cavity - no L blocks - engineer designed

using just 20mm of insulaiton at the window is a cold bridge which is perfect for the formaiton of condesation

As we are all saying - get someone who knows how to design this stuff

sydthebeat

about2build wrote: »

Thanks guys, i've done that and been told thta an L block is needed for structural reasons but that it will only cover 50mm and that the other 100mm should be filled using a cavity closer. He also recommends keeping the L face back 20mm from the outer leaf so as to facilitate an insulated board to also be fitted...
what ya think guys

in "olden" days window frames were screwed through the frame into the wall.
Therefore blockwork was required at the plane where the window was installed. the glazing was then installed into the open frame.

Today all windows are fixed by brackets which are screwed to either the inner or outer leaf, or both.

In 12 years of inspecting house construction ive only ever seen one house build with proper L blocks. Personally i do not see the requirement for them unless the opening is so huge that the frame actually required direct fixing to blockwork eg large slider doors. I have yet to see this being required on a domestic build.

If you are in doubt, ask a structural engineer if they are a strict requirement or not for the openings you have.

braftery

Hi all,

Wide cavity construction (200mm/250mm) is becoming more common.

It is not good practise to fit windows with simple standard straps in cavities this wide. The strap can not hold the window in a stable manner.

Placing plywood across the cavity appears to the current popular method for creating a stable platform to install against.

Whatever method you use .... if you do not draw out the final wall build up and consider all of the potential problems you are leaving yourself open to all kinds of problems down the line.

Window openings near corners can present problems for the guys on site that a drawing may not make apparent.

And finally ... after the detail is worked out ... the actual block laying on site needs to be checked at the very least on a daily basis, to make sure that the block layers are actually following the detail in all of your openings.

In the last two weeks I have been on three sites using this 18mm plywood method .. to make this work properly .. the inner block layer needs to be stepped in 20mm on each side and the inner lintel needs to be raised 20mm above the outer one. The block layers on all sites had been given a detail drawing making all of this clear and in all of the sites there were openings that were not correct. On one site the block layers had to pull down an entire wall and rebuild it.

Planning and supervision is the only way a build will go well, and it seems this is the place that everyone cuts first from thier budget.

about2build

I have asked an engineer and my architect as well-this stuff im posting isnt coming from block layers alone apart from what was in the original post.
most recent suggestion was to open the inner leaf by 40mm more than outer leaf opening so as to facilitate 30mm + of rigid board in the reveals on the head and under the window boards and thus closing the cavity and certainly not creating any thermal issues....meeting an insulation expert tomorrow and going to ask him about the advantage of the cavity closers method and see if it stands up.....really appreciate the debate though guys and keep any thoughs coming. i gues there is no one definitive way to go but once established it must be ensured it is adhered to on site

sydthebeat

just to be clear... i have no issue with L blocks being used once they are the proper proprietary blocks and not cut blocks. I would just personally question the requirement for them, given the downgrading of the thermal performance and the obvious extra costs of the blocks. It is undeniable that a full full insulation detail is a better thermal detail here, so that leaves mainly structure as the issue. So if the architect / enginner is insisting from a structural point of view then i certainly wouldn't go against him/her. After all they are they ones taking responsibility and so they are absolutely allowed to be conservative.

PS... i love the term "insulation expert"... is there a level 8 course you can do to get that designation??? :P

sinnerboy

sydthebeat wrote: »

PS... i love the term "insulation expert"... is there a level 8 course you can do to get that designation??? :P

No . you need only be a rep for an insulation company , attractive to many punters because advice is "free".

braftery

sinnerboy wrote: »

No . you need only be a rep for an insulation company , attractive to many punters because advice is "free".

Nothing wrong with Free advice ..... as long as you are expert enough to know if it is also suitable advice.

is that a riddle wrapped in an enigma wrapped in a .......

about2build

Thanks guys and ya Syd i guess i deserved that one eventhough in fairness to the man I met he was pretty knowledgeable and the free advice was worth it!!!
I want to go with a 40mm stepped back inner leaf and wrap around dry lining into the reveals and on head with raised lintel and under board. Only issue i have to establish is how windows can be fixed in such a scenario and if they are to be attached to the outer leaf them will that cause perforation to the DPC?? Any thoughts on either of these guys? Contacting window company as well for advice

mail

Hi what was the measurements on your plans for the wndow opes? The person who designed the house should have all this detail on the drawings. The measurement on the window or door opes should be on the plan as in 1800mm external leaf 1840mm inner leaf. it is unfair to blame the tradesman who is only going according to the measurement on the drawings. Furthurmore there are bad blocklayers who havent been trained properly, but also very good tradesmen who are well up to the modern building requirements, alas they are all branded the same as if they only build lego blocks and havent got a clue why they are doing it that way. My thoughts on your situation would be to bring the insulation in the cavity out to the window ope, fill the full jamb with insulation including the vertical DPC, and use your insulated slab around the ope including the head. The window is then measured with a 5mm gap around which is filled with expanded foam to hold the window in place until the external and internal reveals are in place. In this situation there would be no need for L blocks. It is most important that the window frames are measured tight, some companies allow too much to make sure the window goes in easy. Dont be shy to make sure the blocklayer knows how important it is to keep the opes plumb, but if you choose the right person there will be no need to tell him as he will be well aware how important this is.

about2build

Thanks guys and no the architect did not go in to that detail on the drawings...in line with what you were saying the block layer is very much tuned in and up to date and when i said no to L blocks he came up with other options. I spoke to the window company and they maintained no problem with fixing the window in place and they are a well known firm so accurate fit shouldn't be a problem....I am thinking of going with something very similar to what you have suggested mail and other contributors thatks again