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How to close cavity after windows and doors have been fitted


  • Registered Users Posts: 534 ✭✭✭ SC024

  • Registered Users Posts: 2,263 ✭✭✭ Yellow_Fern

    Would have been better if the door was more over the insulation.

    Perhaps paint the blockwork and tape on it. You may need extra sealant. Make sure you use the correct tape if you want to plaster over.

  • Registered Users Posts: 751 ✭✭✭ C. Eastwood

    Do not paint the concrete blocks.

  • Registered Users Posts: 2,263 ✭✭✭ Yellow_Fern

    This article is not for your situation as such but I think it offers some useful thoughts

  • Registered Users Posts: 751 ✭✭✭ C. Eastwood


    This cavity should have been closed with “L” blocks, which are built in to the inner leaf. See photo.

    Here are some details from Homebond House Building Manual.

    Your detail is fine.

    The Airtight membrane can be fitted over the insulation.

    The plasterboard slab reveal can be fixed mechanically to the concrete block and plastered with a 3 mm plaster skim.

    The windows and door frames must be fitted with the outer face of the frame in line with the inner face (back) of the outer concrete block leaf.

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  • Registered Users Posts: 1,285 ✭✭✭ dathi

    you will find the acceptable construction details, ACDs 2021 in the above link which give the current details .the book used by previous poster was printed 20 years ago and doesn't take into account the many changes to the regulations in the intervening years

  • Registered Users Posts: 751 ✭✭✭ C. Eastwood


    The Homebond House Building Manual 7 th Edition was printed in 2012 see photo.

    It is the current edition.

    It was printed 10 years ago. The 8th edition is coming soon.

    The House Building Manual is given by CIF to all Building Contractors.

    It’s best to ascertain actual Facts and not make the facts up, and give persons on the forum false information.

    The details given in the photos from the Manual are excellent details.

    I would not all a Building Contractor to use the detail that you put up, as there is no concrete block cavity closer shown.

    Your detail is not in accordance with Homebonds details.

    I will let you in on a little secret not divulge by Google - the purpose of the Cavity Closer concrete block is to provide a perfect secure fixing for all external door frames.

    In your detail (please don’t mention Cold Bridge and / or Thermal Bridge) would allow the plaster on the internal reveal crack at the frame, every time the external door is allowed to slam closed.

  • Registered Users Posts: 666 ✭✭✭ CreadanLady

    dont use L blocks any more. they give a cold bridge or at least, an area with much poorer insulation

    use expanded metal over the cavity and rener and skim in normal way

    or put a slab over it

    The MFV Creadan Lady is a mussel dredger from Dunmore East.

  • Subscribers Posts: 37,746 ✭✭✭✭ sydthebeat

    Mr Eastwood

    if you think the provision of the Acceptable construction details is providing "false information" and you are espousing homebond details first published in 1993, then im afraid it goes to shown how completely out of touch you are with contemporary building practise are in ireland. Please dont accuse other posters of making up facts. In case you dont know, the 'acceptable constriction details', whilst nowhere near perfect, are a requirement to comply with the 0.08 thermal bridging factor to be inputted when determining compliance with Part L of the building regulations. if you built to those (wildly out of date) homebond details, you would have to consider the thermal bridging factor as 0.15. If you do not know what that means in reality, it is saying that the thermal bridges of the house are causing almost 50% more heat loss than if constructed to the ACDs

    I am in the industry, full time, since 1999 ... been involved in literally 1000's of house builds, and i can tell you that i have only see L blocks used once in that time, by a contractor building his first house. He had to order the block in specifically from the concrete company as they had none in stock because no one used them.

    you need to understand why they were first created and used, and then the subsequent changes in window and door construction as to render them not essential anymore.

    The designers of the most contemporary, detailed, analysed and synthesised buildings constructed today (Passive houses) would laugh at you if you brought that detail to the table.

  • Registered Users Posts: 751 ✭✭✭ C. Eastwood

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  • Subscribers Posts: 37,746 ✭✭✭✭ sydthebeat

  • Moderators, Regional North West Moderators Posts: 43,860 Mod ✭✭✭✭ muffler

  • Moderators, Regional North West Moderators Posts: 43,860 Mod ✭✭✭✭ muffler

    Very mature. As I said before you need to grow up.

  • Registered Users Posts: 666 ✭✭✭ CreadanLady

    I am with @sydthebeat on this one. L blocks are totally obsolete and are a massive cold bridge feature.

    The MFV Creadan Lady is a mussel dredger from Dunmore East.

  • Moderators, Home & Garden Moderators Posts: 10,110 Mod ✭✭✭✭ BryanF

    Home bond book.. This explains a lot.

    im with syd on this.

  • Registered Users Posts: 37,610 ✭✭✭✭ Mellor

    To answer your question.

    The best way to close the cavity is to remove the window. Install a closer and reinstate the window in the correct location. Hard to tell from the photo, but may be in the wrong spot, slightly.

    They're are other ways you can rectify, but you asked for the best way. Any other way would be compromising imo. If your builder did this, it would be time to be a prick, or have your design professional be a prick, and make him do it right.

  • Registered Users Posts: 1,651 ✭✭✭ DBK1

    For a man who on another thread recently was arguing over the extortionately high prices you charge for engineering being down to the value of your time and quality of your work, to then refer to an engineering handbook first published 30 years ago and the latest update being over 10 years old is laughable and shows exactly what’s wrong in the building profession these days.

    OP, or anyone else reading this thread, under no circumstances should you ever allow a shoddy block layer, or engineer, instruct you to use L blocks. When it comes to air tightness and cold bridging it’s the worst of all the options for detailing around windows and hasn’t been done in over 20 years. It is nowhere near meeting the standards required for Part L regulations.

    Concrete blocks are the most porous material used in construction and under no circumstances should a concrete block be allowed “bridge” from the outside to the inside or you will have damp spots forming on your inside walls in a very short period after the house is sealed, if you could go so far as to call it sealed with them being used.

    I’d be very worried for any of your clients C.Eastwood if this is the type of out of date advice you’re giving to them. I hope if you have houses currently under construction, where this detailing can still be changed, that you’re man enough to now go to the owners/builders and admit to your mistake and get them changed before windows are fitted.

  • Registered Users Posts: 4,426 ✭✭✭ maestroamado

    Do you know if there was a damp-proof strip put on the inside wall... assuming there was the plasterer will take care of and advise... i would suggest digging out a small amount of insulation and filling with plaster with waterproofer in it... nothing like wood as this a magnet for to draw in mousture...

  • Registered Users Posts: 72 ✭✭ SodiumCooled

    I have been reading the discussion since we are building ourselves at the moment, interesting to read. I checked our drawings and thermal L blocks (e.g. Quinnlite or similar) are specified to close most of the cavity and with the final 100mm closed with a section of insulation.

  • Subscribers Posts: 37,746 ✭✭✭✭ sydthebeat

    slightly different as those quinnlites dont actually "close the cavity"

    They have a 75mm return, which means in a standard 150mm cavity theres still 75mm of a cavity to be closed off (typically this is done with 75mm Rigid insulation friction fitted into the gap between the inner and outer leaf.) In the vats majority of cases where there is 150mm cavity with no return block, The cavity is closed off with 150mm of Rigid insulation friction fitted (if partial fill, or pumped insulation is specified)

    In the photos above it looks like there is 150mm full fill board insulation used in the cavity, therefore there is no cavity as such to close off. The OP is asking about how to finish the detail moreso than 'closing the cavity'.

    at the end of the day its the structural engineers call if the opening needs a structural block return, which is dependent on what exactly is being fitted into it. Most standard openings for modern windows (strapped) do not require any return from a structural point of view

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  • Registered Users Posts: 72 ✭✭ SodiumCooled

    Thanks, I edited my post as I only had a quick look at first but on closer inspection I can see that they don't close the cavity fully as you said. It's a 250mm cavity and the L looks to be closing 150mm of that with the final 100mm closed with rigid insulation.

  • Subscribers Posts: 37,746 ✭✭✭✭ sydthebeat

    ah yes, a 250mm cavity cetainly isnt standard, and needs specific structural engineering solutions.

    very few window manufacturers who will stand over the structural stability of a window being strapped back over 350mm to the inner leaf, so a return makes a lot of sense in your case.

    i havent seen a quinnite with a return greater than 175mm though, are you sure you can get one with a 250mm return in order to only leave you with 100mm to pack? if youve to get these made to order they could costs a fortune.

  • Registered Users Posts: 4,426 ✭✭✭ maestroamado

    Does this mean that the original post shows correct work and it just needs plaster over like i said earlier...

  • Registered Users Posts: 72 ✭✭ SodiumCooled

    I don't know if they are available is the honest answer, looking on line doesn't return any hits for them. We haven't started the blocklaying as yet so all I have been pricing is standard blocks - the finer details I haven't yet discussed with the Architect and blocklayer. It is just this conversation that highlighted this detail so I went looking at our own drawings. Looking at the drawing it is certainly suggesting the a Quinnlite cavity closer is closing all but the final 100mm of the cavity though maybe its just represented that way, according to our architect 250mm is becoming much more common now even some people going for 300mm cavity so he must have something in mind for it as he would know his stuff.

    I will be meeting with the blocklayer onsite about 2 weeks before he is due to start so there will be time for highlighting these details and having any back and forth with the architect.

  • Registered Users Posts: 290 ✭✭ Biker1

    There is no need to go above a 200mm cavity in this country as the climate doesn't warrant it. As for using Quinnlite blocks around windows an doors, waste of money. If a cost benefit analysis is done then it is plain to see the savings in heat loss would mean it could take 100 years to recoup the extra cost. Just return the standard blocks to 100mm from the outside leaf and close the rest with PIR insulation. This way you have no thermal bridging, plenty of block to strap the windows to and the airtightness tape can be plastered over right up to the window frame. Proprietary cavity closers are very difficult to deal with when it comes to airtightness.

  • Registered Users Posts: 72 ✭✭ SodiumCooled

    Just to briefly follow up on this since it may be of benefit to someone else. As you indicated in your post and I found out myself there is no L block with a return to close this cavity. I was speaking with my blocklayer and he said to close this cavity he will just be cutting/breaking a block (be it a thermal block or a standard block) to the right size and laying at right angle to close the 150mm up to the rigid insulation, essentially making the L himself with separate blocks.

    As an aside (prompted by a poster above and some other people I have spoken with) I am having a back and fourth with my architect on whether I can just use normal blocks to close the cavity rather than thermal since there is still 100mm of insulation so should be no thermal bridge and the blocks are so much cheaper.

  • Registered Users Posts: 751 ✭✭✭ C. Eastwood

    I would not be taking instructions from Masons.

    Adding on a piece of a concrete block to make an ‘L’ block will result in mortar droppings in the cavity which cannot be removed.

    This is the reason for using ‘L’ blocks.

    I would not allow any mason to use this old fashion method

    The mason/ builder saved money by not purchasing the ‘L’ blocks.

    See photo.

    The piece of 50 x 50 timber in the photo where the cavity between the outer leaf and the ‘L’ block is closed with insulation is a temporary door frame.

    There is no cold bridge.

  • Registered Users Posts: 72 ✭✭ SodiumCooled

    Hi, and thanks for your response.

    I am not taking instructions as such I am just explaining how the cavity will be closed as explained by my blocklayer based on the drawing from my architect. There are no L blocks available with a long enough return to partially close my cavity to 100mm and there are no L blocks at all (from what I can see) available from Mannok (formerly Quinn) which are specified to be used with the final 100mm closed with rigid insulation.

    I am sourcing all materials myself including blocks, I have no building contractor so there is no one avoiding L blocks - they just don't exist in a size to meet my requirements. The saving money decision I have is whether to just use the thermal blocks at all - they are about 3 times the price as a standard block. Blocklaying will start in about 3 weeks so I need to make this decision in the mean time.

    As for mortar droppings not seeing the issue here - not sure why a good blocklayer would be dropping more mortar laying in this way rather than an L block or laying any of the blocks and also are some mortar drops really much of an issue?