New Roof Design

Hi There, Well I 'm glad to say that I have nearly finished the frame and the inspectors will be here in a couple of days, hope the frame passes....!!! I have a question on the roof cladding. In terms of roof construction see picture I have been thinking of using chipboard instead of MDF as it is quite a lot cheaper. I must point out that there will be a 350 m/m air gap between whatever sheet material I use in the roof design. I already know that MDF is better acoustically, however, I was thinking that because of the 350 m/m air gap, could get away with chipboard and would it make that much difference in terms of isolation and mass. Mike in Melbourne

you might be better off with 2 layers of 5/8" (16mm) drywall instead of a single layer of Soundcheck™ (cost and effectiveness?) i'd use regular r-11 insulation between the battens and r-19 between the smart joists. save the acoustic grade for treatments.

Hi Glenn, Thanks for your quick reply, I like the idea of using ordinary plaster board for the studio roof. I was also thinking of lining that with a lightweight pine board about 6m/m and then varnishing them. Love the idea of wooden ceiling. What do you think? I would also like to know what you think of what I could do on top of the roof battens? I realise 18m/m MDF would be denser, but the 19m/m chipboard is heaps cheaper about $400.00 dollars cheaper. What would you do considering I will have a 350 m/m air gab between the ceiling inside (one leaf) and the outside leaf? I can also get 33m/m MDF for the outside, but it is $45.00 per sheet with the total cost as much as $900.00. Would be great to have but cost prohibitive.....!!! Like your idea on R11 and R19. I'm guessing the R11 and R19 are your equivalent of our standard roof and wall batts respectively? all the best Mike

As standard building practice goes (USA) MDF is not considered a good product in any area that has potential to encounter dampness or moisture. By design MDF is little more then sawdust and glue. If your roof ever has a leak the affected MDF will simply deteriorate and become a weak area in the roof having potential to cause harm to those that may have to repair it. And it swells if it gets wet...then it crumbles apart. For a roof, OSB or plywood has a better structural integrity, then maybe you could apply MDF under that? Your mileage may vary,

Thanks X space for your help The original idea of the MDF was because MDF is a denser material in terms of acoustics, so to speak and will hopefully keep the drums and bass frequencies inside...!!! However, because of the cost I might just have to use chipboard or yellow tongue, as it's much cheaper. The MDF was always going to be covered in an aluminium foil backed roofing blanket then colourbond sheet (very popular as a roof cladding in Oz) as the final cladding to fight against the raging elements. Thanks again for your comments, all the best Mike

i think for the roof, use whatever is commonly used for roofing... probably the osb or yellow tongue. inside - you could add a layer of wood to finish the ceiling. just make sure its properly bonded to the drywall...

Thanks Glenn, Will do all the best Mike

Hi Glenn Well my roof design has slightly changed and I would like your opinion to see if I have a three leaf system or not. If you look at the pic (colourbond) instead of the chipboard placed on top of the battens, I put the chipboard in between the battens and sealed them, but as you can see there are air pockets above and below the foil backed insulation. Would this act a three leaf system? amounting to iso loss or should I put more insulation and pack it in tight and compress it, ensuring I have one leaf consisting of chipboard, heaps of insulation, and the colourbond? Also in terms of heat in summer i was considering putting in on the underside of the chipboard heat reistant magnezium oxide. any ideas? Mike

how dense is the top layer? if its not too dense then it shouldn't be too much of a problem - is the air gap between them sealed or open (to allow air flow and avoid moisture build up)? if its open, you won't have a significant spring there so it shouldn't act as a third leaf.

Mike - that looks correct - the colourbond is not treated as a leaf as it's open to the outside air, plus it's damn thin. From the studio upwards the layers should go: internal drywall (two layers preferably) (Ist Leaf) resilient channel smartjoist with insulation yellow tongue (two layers if possible within budget.) (second leaf) battens building blanket colourbond. which looks like what you've done. cheers john

Thanks john, I was a little concerned that it was not going to be enough isolation. But I'm relieved that the leafs are ok, and all's well. You said that I should put two layers of yellow tongue down, do you think I could use 6m/m magnesium oxide board. This board I'm lead to believe looks a bit like cement sheeting, but it is suppose to have good sound and heat resistant properties. Did I mention that the smart joist (see pic) allows a 260 m/m air space between the yellow tongue and the R/S channel, which prompts me to ask, will I actually need another layer of yellow tonge or 6m/m magoxide board? If you think the air space is not enough, I can get the magoxide boards 1200 x 900 for $6.00 a sheet a saving of two thirds and can get enough to completely cover the roof as well as all outside walls, say underneath the weatherboards. I'm also hoping that it wont get to hot in the C/R and tracking, so I have purchaced a ducted AC heating and cooling unit. www.opticaltv.com.au/. Just for future reference I purchased a split system for my house some years back and it is very reliable, economical, maintenace free (touch wood) and much cheaper compared to other name brands. Our Auzzie pals may be interested for future reference...!!! Thanks for your confidence and I hope your well, Mike

Hi John, In terms of my inside ceiling design. We previously talked about the ceiling joists going up and inside the smart joists. which I can do. My question is do I still need the resilient channel attached to the lower face of the ceiling joists as the joists themselves would be completely detached from the outside roof frame. all the best Mike