Go to Forum Home Building Design Service voids in TF construction – are they worth the hassle?

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    • #30597
      Anonymous

        Getting down to the nitty-gritty design and cost details of our Silver Standard TF house, are 25mm internal service voids really worth the hassle and expense of that extra layer?

        I appreciate the merit in protecting the vapour barrier both from interstitial condensation and airtightness perspectives where the external walls are penetrated, and that battenning and OSB are pretty low cost materials, but then there's the labour….

        So are service voids really worth the extra cost and effort?

      • #33453
        Nick Grant
        Participant

          I am sure that there needs to be a way of protecting the air barrier/VCL or moving it out of harms way and service voids are one way people use. I really dont believe that its practical to seal around all electrical boxes if these penetrate the air barrier but then does a 25mm void sort that for deep boxes?

          I agree it's a hassle and inelegant, most of the void is unused.

          Interested to see what alternatives people have come up with, needs to consider future DIY as well as initial informed construction.

          Nick

        • #33454
          Nick Grant
          Participant

            I'm not convinced! We used a PE VCL above our ceiling (no services) and I peppered it wih holes just trying to hit the I beams and noggings when screwing up the PB. Once PE VCL does tear its almost impossible to repair against soft insulation backing.

            Even if yu suceed what about someone adding a wall light or extra socket (we put loads, all in the wrong places!!!).

            Few ideas:

            1. 89mm stud structure acts as service void with OSB/ply outside and (rigid) inslation over. Is what we did for our house but is a bit wasteful of space. Could add some insulation on warm side at increasing risk of condensation. (depends on external insulation thickness and 'breathability'.

            2. surface mount services. Bedzed did this in an interesting way with timber service board up wall and along ceiling. They did this becasue the walls were concrete. I like galv conduit but not everyones cup of tea. Hollow skirting etc all possible but not without limitations and risk of DIY hacking in future.

            3. use osb behind plasterboard and special boxes that have a proper airtight gland around cable – is there such a product?

            Anyone else got any tried solutions? It's an important detail.

            Attached is pic of nice detailing with service void in roof. Material draped over truss and purlins during construction to allow continuous layer. Work by Mike Whitfield's team for Architype's new office.

            Nick

          • #33455
            Mark Siddall
            Participant

              Steve,
              You could consider: –
              1) A solid VCL rather than a membrane (i.e. adopt a breathing wall solution using Paneline or similar). Though this solution still favours a service void it is far easier to repair and much more robust in the long term.

              2) I have seen (in a journal) a 750mm high services co-ordination unit consisting: removable panels, routed for electrical boxes, held on gravity battens and sw battens to form sub-frame (say 35mm). All in all its a similar to Nick's skirting solution, but its played up to become something of an architectual feature. (Watch out for light switches if this option is used as they will be above the dado line…to avoid this problem try to ensure that they are on an internal stud wall….shouldn't be to hard with some pre-planning.)
              Above this level plasterboard can be mounted on the solid VCL. (The outlets shallow units are required.)

              Putting the service void in and protecting the VCL will save labour in the long term. If condensation rots the timber frame and causes mold (health dangers from spores etc.) you have to rip the wholing building apart. I read somewhere that there have been cases where this has had to happen in as little as 12 months!

              Mark

            • #33456
              Mark Siddall
              Participant

                Andy,
                When you say that the vapour / airtightness membrane is “on top” of the OSB you mean the room side or the insulation side?

                Mark

              • #33457
                Nick Grant
                Participant

                  I posted some pics of Airtight TF detailing by Mike Whitfield (see above) who helped us with our house. He has just done his first pressure test and got a very respectable 1.3 m/hour permeability despite leakage around a temporary door and French windows in need of adjustment.

                  Mike has agreed to give a presentation at the 2007 annual conference with plenty of pics or details often worked out on site. Should be very interesting. Nice mix between chunky green oak crucks and superinsulation/airtightness.

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