(Old question) External vs internal insulation for outbuilding

Discussion in 'Eco Talk' started by BikerChris, Nov 13, 2019.

  1. BikerChris

    BikerChris Active Member

    Hey all,

    Sorry about this, but searching the internet for this just brings up companies wanting to sell stuff.

    So i reckon that external insulation must be better for keeping a constant temp inside and avoids getting hot directly from the sun on it. anyone know if thats right?

    This is for an outbuilding I've mumbled about on here a few times and i'm getting closer to having the time to do it. after renting an office that is always too hot in summer and too cold in winter, i wanted to do something that is bearable all year round. A possible bonus is that if I run short of money, i can do up the inside, membrane external and then wait until money is available....don't like the idea of doing that of course, but if needs be and all.

    Cheers!

    Chris
     
  2. rogerk101

    rogerk101 Screwfix Select

    If you have a choice, always go for external insulation. It doesn't occupy valuable internal space, it eliminates thermal bridging where internal walls meet external ones, and generally it does a better job of keeping temps relatively constant because of the thermal mass of the walls. The only time it's not great is if you use the space very sporadically and for short durations. Then you want low thermal mass, such that the room warms up quickly when you need it warm and then when you leave the room you don't care how quickly it loses heat because you're only coming back to it in a day or two, by which time it's already cooled down again.
     
  3. BikerChris

    BikerChris Active Member

    Wow...Roger thank you that is so helpful. I'm no scientist but I did think that if masonry is internal then it might hold onto the heat well, a bit like storage heater bricks. It's going to be used by either me or someone else so its ideal to be able to keep it at the same temp during the day and may be dial it down in the evening/night. I guess I'd fiddle with heating to get a good balance.

    Really appreciate the confirmation though, especially so quickly. :D
     
  4. glob@l

    glob@l Active Member

    Cost may be a consideration though, in which case internal insulation should work out cheaper?
     
    BikerChris likes this.
  5. rogerk101

    rogerk101 Screwfix Select

    I've done a lot of both over the years, and this has not been my experience. The full price depends far more on the final finish applied to the wall than on whether you insulate internally or externally.
     
  6. BikerChris

    BikerChris Active Member

    Very good point, as you can imagine it takes a lot of effort to do something like this so i don't want to build it and then regret. If money is a problem, so long as its in decent enough condition to use, that is good enough for me. Some bits I can do as money permits.

    I guess if you were paying someone to do it, may be the external would take more labour...may be? Seems I've got to render over EWI, along with some other stuff to keep it attached. I'm not going by personal experience and stuff on the internet. By nice to hear your thoughts Roger.
     
  7. rogerk101

    rogerk101 Screwfix Select

    I've just insulated my single skin brick garage externally with 200mm of insulation followed by and air gap followed by 225mm wide feather edge timber cladding. It came out a real treat and is really cosy!
     
    BikerChris likes this.
  8. BikerChris

    BikerChris Active Member

    Wow, I'm not surprised it's cosy, nice one! Be interested to know what you think of this (in to out): timber panels on 2 inch service batten on low density blockwork (Celcon Block Solar Grade), then something to stick 100mm insulation onto external face, then as you've done, feather edge on batten

    So you fixed through feather edge, batten (air gap), insulation and into brick work?

    I've still got to price up the celcon solars, we'll see eh!
     
  9. rogerk101

    rogerk101 Screwfix Select

    No.
    My insulation panels are 600mm wide and 100mm thick.
    I first screwed a whole lot of 4x2s vertically onto the brick wall using 150mm screws and 10mm wall plugs. They were spaced the exact width of the insulation panels, so 600mm gap between them.
    I then installed the panels vertically between them.
    Then I screwed a whole lot of 4x2s horizontally into the vertical 4x2s, again using 1500mm screws. These were also spaced the exact width of the insulation panels, so 600mm gap between them.
    I then installed the second layer of insulation panels horizontally between them.
    The next 'layer' was the air gap, which I created with roof tiling battens (25x38), which I nailed vertically into the horizontal 4x2s.
    Finally I nailed the 225mm wide feather edge boards onto the tiling battens with a 50mm overlap, so 175mm exposed.
     
    BikerChris likes this.
  10. Bob Rathbone

    Bob Rathbone Screwfix Select

    Chris, if your office is to be intermittently occupied a quick warm up would be preferable with little thermal lag or storage. To attain this put the insulation on the inside.
     
    BikerChris and rogerk101 like this.
  11. BikerChris

    BikerChris Active Member

    Ahhhh, wow x2, that should do the job eh! Thank you for explaining really helpful.

    I am not that good with computers but is the attached what you have done?

    Am I right in thinking that the thermal bridging of the 4x2's is so small it is not a problem? Are you leaving the brick exposed internally?

    I'd love to do that but I only have room for thinn wall (narrow garden), otherwise I kill a lot of space inside :(

    I was originally thinking about insulation mechanically and adhesively (yes not a word) attached to external wall face, then tile batten over and weatherboard finish, just to avoid thermal bridging but may be I'm being over the top with that worry? Also that means I need screws that can go through 25mm of batten, 100mm of insulation and at least 50mm of the brickwork...although you are OK with 10mm into the brickwork?

    Sorry about these questions mate, much appreciate your comments.
     

    Attached Files:

  12. BikerChris

    BikerChris Active Member

    Cheers Bob, much appreciated. I am allowing for the office to be used 5 days a week and may be the odd night so thought it best to have masonry / floor slab hold heat. I would definitely go internal insulation if it was only used for a few hours a day and not that often. I would have space heaters to get it up to a decent temp, use the space then turn it off and leave. There is also going to be some computers in there and a few guitars which I do not think like temp flukuations . Have not played guitar for over 6 years but can't store them in house with kids about lol!
     
  13. rogerk101

    rogerk101 Screwfix Select

    Those pictures are exactly what I've done. Where did you find them?
    C24 wood is a pretty good insulator, so not likely to be much of a thermal bridge. In fact the first layer (vertical columns) of 4x2s are entirely insulated by the second layer everywhere except where the second layer of 4x2s mount onto the first layer ... so a few dots of 47mm x 47mm every 600mm. Not enough to be concerned about.
     
    BikerChris likes this.
  14. shaung383

    shaung383 New Member

    Hi all, I dont know if I'm in the right place here for this question but anyway I'm currently planning to build a 8x12 foot shed in the garden and wanted to insulate it so I can use it as a workshop all year round, I'm going to build it from 3x2 timber so the gap in my walls will be 75mm, now I've looked at insulation board and rockwool and think I'm going use rockwool as is alot cheaper and apparently better for sound damping, my question is though is it ok to put 100mm insulation in a 75mm gap and pack it in or will it not make a difference, I'm hoping if I do it will keep it warmer in winter and itl be thicker so hopefully itl sound proof it more, any help is much appreciated thanks in advance.
     
  15. JustPhil

    JustPhil Active Member

    Compressing insulation is advised against by the mfr’s, problem being it’s the trapped air in rock wool that does most of the work in terms of thermal insulation, so when you squeeze it down you’ve got less trapped air. However, so long as you expect it to perform only as well as 75mm insulation I think it’s ok. It may improve sound insulation, as that function is more based on density than air trapping.
     
    shaung383 likes this.
  16. shaung383

    shaung383 New Member

    Ok that's good to know thanks for that, soni dont need to worrie about having an air gap either, I can just fill the wall with the wool
     
  17. JustPhil

    JustPhil Active Member

    Just seen you’ve started your own thread, I’ll follow up there.
     
  18. BikerChris

    BikerChris Active Member

    Ah great, I got the gist - I made them images with some free 3d software.

    yeah i did think that the thermal bridge area would be tiny and when you have as much insulation as you, like you said not worth being concerned about.

    What do you think of my idea? No thermal bridging but only 100mm insulation?

    Thanks again.
     
  19. rogerk101

    rogerk101 Screwfix Select

    I insulated a house externally in the French Alps 30 years ago by sticking 100mm thick insulation boards onto the rendered wall using a specially formulated adhesive. Once the boards has stuck correctly, I rendered it with a fibreglass mesh for the first coat and then a coloured, textured flexible but rigid render as the final coat. I still have the house and still go there for winter sports, and it's really cosy ... which it wasn't before I added the external insulation 30 years ago.
    In other words:
    100mm might not be great, but it certainly has an impact
    external insulation works well and lasts a long time
    whatever I paid for it way back then has long since paid for itself ... in fact I'd say it paid for itself within the first 5 years
     
    BikerChris likes this.
  20. BikerChris

    BikerChris Active Member

    Thank you for that Roger, you're a good egg. If I can push the insulation thicker I definitely will. At the moment I've got a garden 5.8m wide with close boarded fencing either side, so I'm putting the final external face 350-400mm from the fences. So this gives me a potential 5m over all width, though it's an L shape building that is also around 3.4m'ish.

    Thanks again for your comments mate, really appreciated.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice