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Lean to timber frame side kitchen extension

Discussion in 'Roofing and Guttering' started by ReX83, 20 Feb 2020.

  1. ReX83

    ReX83

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    Hi all,

    My house (victorian middle terrace) has an extension built at the back of the original kitchen, leaving a sort of courtyard in the middle of the structure. I'd like to close this space with a lean to timber frame extension with double glazing on top, similar to his:

    [​IMG]


    What kind of timber should I use to have smooth and plane surfaces (with square edges) and excellent stability?

    I suppose the classic C24 regularised carcassing timber won't be very appealing. I was looking at PSE / PAR timber but I can't find any information in term of structural capabilities. I read that Douglas Fir is often used for exposed rafters.

    I would like this type of finish:

    [​IMG]

    The only company I've found (https://www.patent-glazing.com/rafterline-patent-glazing-bars.html) providing a glazing system that can sit on top of timber rafter, requires 44mm rafters able to support 320N/m².

    BTW - I am still pondering if I can do the whole timber work on my own (and get the glazing company to install the glass roof) or hire someone.

    I forgot to mention that the wood shouldn't be exposed to water and humidity: the rafters are sealed on top by the double glazing structure and the timber on the side will be fixed against a single leaf wall made with Thermalite blocks (or similar).

    Thanks!
     
    Last edited: 21 Feb 2020
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  3. Ryler

    Ryler

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    The rafters in that image alternate between side and top supported on the posts.
    Only reason I can think of is aesthetic feature.
     
  4. ReX83

    ReX83

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    If I understand your point, yes, I appreciate that in the second photo the rafters are not supporting the glass.

    To clarify, the structure I am going to build will be like in the first picture, with rafters supporting the glass panes, but I want wood with the finish of the second picture (brighter than the first pic).

    Any suggestion for structural smooth wood to use for this application?
     
  5. Ryler

    Ryler

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    Red cedar maybe.
    Douglas fir.
    No idea tbh.
     
  6. Notch7

    Notch7

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    the most common system is exitex capex

    https://www.questhardware.co.uk/sea...em/capex-glazing-bars/capex-5070-glazing-bars

    basically you need a rafter gasket on top of the rafter, then the glass, then your capping

    all the timber is internal

    NB: at the lower end you should have the rafter gasket running out beyond the end of the glass (typically this requires a cut out at the fascia) -its important as it allows the system to be drained if it leaks and allow condensation to run out.

    double glazing has a 12mm seal around the edge -and the capping bar must cover that externally as the seal can break down if exposed to sun. Typically allow the glass to go over the rafter by 15mm.

    timber choice -a bit tricky

    if you want pine, then you need unsorted grade (mixed grades 1-4), often known as joinery grade. Be aware that sections like you want, say 50 x 125, 50 x 150 are likely to contain the heart and are prone to splitting

    you could use douglas fir but beware it is prone to resin pockets and may also have splits


    if you are going to paint then I would suggest hardwood, either meranti, sapele or red grandis
     
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  7. ReX83

    ReX83

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    Thanks, the Capex system looks very simple to install, compared to the one above.
    I'll see if I can find drawings, I have few questions: e.g. how is the bottom of the glass going to be covered? I suppose the top will just covered by overlapping lead flashing.

    Regarding the wood, if I get "simple" regularised untreated C24 softwood and varnish it, is there any issue with that?
    I have seen some shops having very smooth and square C24 timber.

    Why hardwood only if painted? Varnished would be fine?
     
  8. DIYnot Local

    DIYnot Local

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