Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

Buy individually or both books together. Delivery is free!


powered by Surfing Waves




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




    • CommentAuthorthebeacon
    • CommentTime6 days ago
     
    Hello,

    I’m planning to build a wood workshop in my garden and would like to hear people’s advice on thermal bridging.

    I’m planning to use ground screws as the foundations, with 100x45mm timber walls with the interior walls being exposed birch plywood. The wall build up will be as follows:

    Interior:
    11mm birch ply
    1mm Vapour Control Membrane
    100x45mm timber stud (with 90mm PIR insulation within the stud
    11mm OSB board sheathing
    1mm Tyvec firecurb membrane
    25x50mm vertical timber batten
    25x50mm horizontal timber batten
    20mm timber cladding/ of potentially a different material

    My question is, should I be concerned about thermal bridging.

    Thanks in advance,
      image.png
  1.  
    How often will you be heating the workshop and to what temp. and what will the typical outside temp. be at those times?
    • CommentAuthorthebeacon
    • CommentTime6 days ago
     
    I plan on using it all year round, to make picture frames and store photographs. I don't particularly want it to drop below 10 degrees. But it will be more like 18 when I'm working in it. I'm based on the south coast of the UK, the coldest it normally gets is -3 at night. in the winter it could be around 3-8 degrees outside in the daytime when I plan on using it.
  2.  
    If you are going to store photos in the workshop will a stable (or min/ max) RH be needed? Also if you don't want the place to drop below 10deg. then some sort of heating will be needed on a thermostat for unoccupied times. (The design is a light weight structure so minimal thermal mass to store and post use heat).

    I would not expect the cold bridges to be an issue if you are maintaining a 10deg. minimum other than additional heating cost.

    The cold bridges could be mitigated by an additional 2 -5 cm insulation (more PIR or EPS) between the internal VCM and (over) the 100mm stud work with the 11mm ply fixed through the insulation to the studs. This would also give additional insulation to mitigate the heat loss.
  3.  
    The cold bridging issues will be at lintels, and the junction of wall to floor and roof. Those need some thought or they can end up horrible. Do the same sort of section drawing, but for each of the nasty interfaces. That will also make you think through the construction of those parts, to simplify them.

    Cold bridging, has 2 issues - heat loss, and potential to induce condensation. You've low moisture generation in workshop, but cold night followed by mild damp day, could cause a cold spot to condense the mild damp air that comes into the workshop from outside. Keeping the interior warm (at least the 10oC you mentioned) will mitigate that, but be more energy intensive.

    Are you going to run services on the surface? Seems a shame to go to the expense of Birch ply, which has increased massively in price, and then fix surface trunking/sockets/lighting. Consider PiH suggestion of a layer of insulation over the studs internally, then VCL, then timber batten (service void), then ply. Actually, that additional layer of insulation could go on the outside (over the OSB), then VPM, then batten layers. Keeps the studs and OSB a bit warmer. Personally I'd use 25mm. That will cover all the unavoidable solid timber parts.

    Remember to foam all the edge of the rigid insul around the studs, or where you butt 2 pieces.
    • CommentAuthorJonti
    • CommentTime5 days ago
     
    Wouldn't EWI be the best way to avoid thermal bridging? This would be easiest to do as well.
    • CommentAuthorthebeacon
    • CommentTime5 days ago
     
    Thank you for your suggestions.

    Posted By: Peter_in_Hungarythen some sort of heating will be needed on a thermostat for unoccupied times.


    I am planning on installing a heat pump with a heater that's also a dehumidifier: https://www.airconcentre.co.uk/products/powrmatic-vision-3-1dw-h-air-conditioning-and-heat-pump-vis3-1dw-h. That should also help maintain a RH.



    Posted By: GreenPaddyAre you going to run services on the surface?
    Yes, I'm planning on running all the electrics on the surface in galvanised conduit. The birch ply is the desired material, the budget might force me to install a cheaper ply.

    The addition of 25mm insulation over the stud work makes sense. The decision is whether it goes on the internal or external. My preference may be external, to gain the extra floor space. Good to know it could go on top of the osb.



    Posted By: GreenPaddyDo the same sort of section drawing, but for each of the nasty interfaces
    that's a great suggestion. I will do this to consider the best way to mitigate these potential problems.
    • CommentAuthorSimonD
    • CommentTime5 days ago edited
     
    Posted By: JontiWouldn't EWI be the best way to avoid thermal bridging? This would be easiest to do as well.


    Yes, it would. That would get my vote. :wink:
  4.  
    I would also normally suggest that EWI as a better option unless foot print (due to planning constraints) and maximium internal space are issues
    • CommentAuthorSimonD
    • CommentTime5 days ago
     
    Posted By: Peter_in_HungaryI would also normally suggest that EWI as a better option unless foot print (due to planning constraints) and maximium internal space are issues


    True. If space is a big problem, perhaps the design could be turned properly inside out and use reduced stud sizing to boot:

    1. lose the internal birch ply
    2. studs (2 x 3 at e.g. 400 c/c)
    3. sheath with birch ply (keeping inside face visible internally) and forget the osb.
    4. vcl (if even needed)
    5. insulation
    6. breather membrane
    7. battens
    8. cladding

    The free space within the stud now gives service void and shelving space etc.

    By now you've almost lost the extra depth of ewi through the wall buildup and reduced the thermal bridging.

    Just chucking out ideas.
    • CommentAuthorthebeacon
    • CommentTime2 days ago
     
    Thanks for all the suggestions so far.

    I have drawn up some more plans, taking on board the advice.

    Posted By: GreenPaddyActually, that additional layer of insulation could go on the outside


    Posted By: Peter_in_HungaryI would also normally suggest that EWI as a better option unless foot print (due to planning constraints) and maximium internal space are issues


    I have added 25mm external insulation on top of the OSB boards to help limit any thermal bridging. I have also run this EWI down to the floor joists.

    Because of the narrow width of my garden, the studio will be placed within 1 metre of the boundaries, which means i will require planning permission. I will keep the interior floor space to under 14sqm. It will be roughly 3.5x4m.

    i want to keep the build under 3m in height. keeping the build under 2.5m would mean I skimp on insulation and the strength of joists. Due to height restrictions, I will build a flat roof with a 1:60 fall. Does anyone have suggestions for a decent material to use? it looks like EPDM is the main type people go for these days.

    At the moment I have the floor insulation exposed below the joists, is it advisable to cover this? i plan on cladding down to the floor level.
      second1.png
    • CommentAuthorthebeacon
    • CommentTime2 days ago
     
    Here is an image of the floor:
      secondfloor.png
    • CommentAuthorthebeacon
    • CommentTime2 days ago
     
    Here is an image of the roof:
      secondroof.png
Add your comments

    Username Password
  • Format comments as
 
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press