Replies

1. 
   dgbldr | Feb 15, 2006 08:22pm | #1

    need advice on what components to use when installing metal roofing over a tongue and groove roof deck in a rainforest environment.  The roof deck will be of native hardwood that will be exposed to the interior.  I had thought that using a silver backed bubble type insulation about one-eighth inch thick over the roof deck followed by a half inch purlin followed by the 24 gauge metal roofing would be sufficient.  The intent had been to use overhead fans alone for interior cooling.  Now it has been determined that the interior will need to be air conditioned. How can I realize the optimum insulation values in this situation?  The bubble wrap with the metal backing seems to be all that is available but I question whether there is much R-value at all.  By the way, the project is in a third (fourth) world country so there is not the luxury of off the shelf components unless I import them.

   The silver bubble has no R value but is good for radiant. If you can install it with a larger airspace between the bubble and metal, it will actually work very well as it will reflect the radiation from the roof.  Obviously if the metal is painted on top with aluminum paint it will work even better.

   Secondly, I am using the same 24 gauge metal siding for the exterior wall covering.  Previously, I was merely going to screw the metal to the 2x4 wall studs without any barrier or insulation and later finish the interior wall with gyprock.  Batt insulation is out in a high humidity climate since it will absorb moisture and droop in time.

   Build it the same as the roof. Bubble, space, metal.

   I have also been told I need to use capped and gasketed metal roofing screws suitable for wood decking.  The recommended method of placing these screws is NOT in the raised profile of the metal sheet but in the channel with the gasket slightly depressed.  The explanation given by fellows near the building site is that the normal placement of gasketed roof screws in the elevated profile of the roof panel typically allows the screws to be over driven thereby deforming the metal and providing entry for water.  They say that the NEWEST and BEST method is to place the screw in the section of metal where the flat metal is in direct contact with components below.  I hope that is clear.

   The advice you received is correct.

   DG/Builder

1. 
   Davestephen | Feb 16, 2006 08:11pm | #2

   Thanks, DG,

   What might use to provide some R-value to the roof and walls, now that it is necessary to AC the interior at times?  Any ideas?

   Dave

1. 
   paul42 | Feb 16, 2006 08:50pm | #3

   spray foam would be my first choice, but might not be an option where you are building.

   Otherwise, shade and ventilation are your only real good options.  White metal roofing and walls.  Figure out how to vent the space between the roof decking and the metal roof.  Vapor barrier between the wood and the metal.  30 lb. felt with lots of overlap would help.  Overhangs of somekind on windows to keep direct sun out. 

1. 
   Davestephen | Feb 17, 2006 04:48pm | #7

   Hi, Paul,
   I have used spray foam in the US and it is a great vapor barrier and insulator. Where the projeect is located it's out of the question. The metal roof and siding are white. There is a six foot overhang of the roof. The rear of the building is exposed to late afternoon sun, which is why we will attempt to insulate the walls as well as the roof.
   I will use the advice of placing the vapor barrier/foam wrap (this has very little if any R-value) on top of the roof decking and taping it at seams. Then I will use 1x2's to give an air space before screwing the metal roofing down. Would the felt be required in this instance? I believe that I should use the same method to construct the walls.
   Your thoughts are appreciated.
   Dave

1. 
   paul42 | Feb 17, 2006 05:09pm | #8

   I would still put the felt underneath the foam wrap and I would overlap each layer about 50%.  The foam wrap provides a good air infiltration barrier, but only as long as the tape lasts.

   Is there any way to plant some vegatation on the west side to protect against the late afternoon sun?  I would try to keep any windows on the west side high up and small to avoid solar heat gain.

   good luck

   Paul

    

2. 
   VaTom | Feb 16, 2006 08:56pm | #4

   Are rice hulls available?  They work very well.PAHS Designer/Builder- Bury it!

3. 
   dgbldr | Feb 16, 2006 09:34pm | #6

   What might use to provide some R-value to the roof and walls

   Whatever insulating materials are available locally. Fiberglas, foam, straw board, anything is better than nothing.  Make sure the radiant foil is on top with nothing but an airspace between the foil and the metal.

   DG/Builder

2. 
   atrident | Feb 16, 2006 09:17pm | #5

     Look at http://www.ebay.com under radient barriers. Also http://www.reflectixinc.com. The bubble wrap has to have some R value but the company doesnt claim any.