Replies

1. 
   JDRHI | Nov 24, 2003 05:31am | #1

   Sounds like you`re a candidate for RAFT-R-MATE....check it out here....available most everywhere.

   http://www.owenscorning.com/around/ventilation/raftrmate_attic.asp

   J. D. Reynolds

   Home Improvements

   "DO IT RIGHT, DO IT ONCE"

1. 
   emerckx | Nov 24, 2003 02:44pm | #2

   Jaybird,

   Looks like the ticket. The spec sheet says for high humidity conditions to put some polyethylene vapor barrier on the "warm" side of the raft-r-mate. Well, in florida, which side would that be? Toward the interior of the building or toward the roof?

   Thanks much,

   Mike

2. 
   dIrishInMe | Nov 24, 2003 04:14pm | #3

   JD's suggestion for retaining airflow is the commonly accepted practice around here too.  There are also heavy cardboard baffles that serve a similar purpose and are better at protecting the soffit vents although they are less readily available.  

   I have a few questions though... Does your shop have an attic - probably scissors trusses?  See example: http://www.galyonlumber.com/example5.htm   Or is it stick framed with 2x8, etc rafters only?  See rafter1 pic below.  Ignore the rafters2 pic, I attached it, but then realized it doesn't pretain to your situation, but couldn't delete it.

   Matt

   
   

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   Edited 11/24/2003 8:34:54 AM ET by DIRISHINME

1. 
   emerckx | Nov 24, 2003 09:19pm | #6

   Thanks for the help. I may not be using the right terms, but I'll try to describe the shop. Half the shop has a small, unfinished attic space with exposed rafters (8 ft from floor). The other end of the shop has what I guess you would call scissor trusses. It's handy because I can store stuff in the "attic" but get to it easily from the open end. I'm hoping to insulate between the trusses or rafters or whatever they are called up against the roof sheathing. That would leave me all the vertical clearance for moving sheet goods and lumber around and also allow me to store stuff in the rafters.

   Mike

1. 
   dIrishInMe | Nov 25, 2003 03:53am | #7

   Roof trusses are generally made in a factory and have metal connector plates that hold the assembly together.  They are brought via truck to the building site and each 'A' shaped assembly is installed on top of the walls.   They most often have 'W' shaped bracing (or other diagonal bracing) that helps stiffen the each truss assembly.

   Rafters are pieces of lumber that are cut and installed on site in an sloped position to support your roof sheathing.  Each board is installed  one piece at a time.  They are most often 2x8s. They are also often used with ceiling joists - the floor of your attic.

   Answering your original question, if you want the insulation up by the roof sheathing, this is the place for the insulation baffles that JD (?) referred to in his .2 response.  This will help prevent condensation from forming on the bottom side of your roof sheathing, which could cause it to rot.   

   If you are going to insulate up by your roof sheathing, look for R-19C or R-30C insulation as it gives more R-falue per inch, and thereby leaves room for the vent baffles.  You also need to have a continuous vent along the ridge of the roof.

   On the other hand, if the roof is built with trusses, the top chord (upper most pieces) are probably 2x4s and do not have enough depth to give you adequate R-value (thermal insulation value).  I believe that a bare minimum of R-19 (5.5" thick) is recommended for FLA ceiling insulation, with an optimum being in the range of R-30 (~10" +-3").

   Really though, the correct way to insulate a building with an attic, is to put the insulation on the "floor" of the attic.  This way, there is not problem with blocking ventilation, you can use loose fill blown in insulation, which gives the most complete coverage, and it is easy to get enough depth in the insulation to meet the above recommended thickness requirements.  Down side is you could not store materials as you now do, and if using blown in insulation, you would need some kind of a finished ceiling (sheet material) installed on the bottom of the trusses.

   I believe that the foil radiation barriers are supposed to be stapled on the bottom of the truss top chords.  The insulation can either go above or below the radiant barrier, (ck manufactures' recommendations) again assuming that you have enough space between the 2by? members that support the roof sheathing for an adequate thickness of insulation.  Really though, if you are going to staple the insulation up by the roof sheathing, you could get foil faced insulation which will give a similar effect to the radiant barrier.

   Maybe though, you should get an insulation contractor to LOOK at what your situation is, get his ideas, and get an installed price.  Not sure what you will find $ wise, but in the new construction business, you can often get an entire house insulated for only a few hundred dollars more than you can buy the materials for - the reason being that a good sized contractor who specializes in insulation gets a volume discount from the manufacturer/distributor.  Plus, unfortunately, insulation workers don't  make a lot of money.

   It will be easy to compare the bid price to the DIY price as all the stuff you need for this project will be available at the big box store (HD?).   Around here (NC) HD even has an insulation blower that you can rent rather cheaply. 

    Good luck,Matt

3. 
   jimz | Nov 24, 2003 08:51pm | #4

   Here in the north, we're generally concerned with heat loss via conduction (that's why we pile on insulation in our ceilings) and losses via convection (why were concerned about sealing leaks into the attics & outside). "Up here", one of our biggest concern is venting attics to remove moisture and the Raft-R-Mate forms do help the air flow from under the soffet into the attic and hopefully out through some sort of roofing ventilation. The forms to prevent ceiling insulation getting into our soffets, thus allowing air movement into the attic (from the soffet). 

   In Florida however, I believe that a most of your heat gain is from radiation (via sun hitting your roof). The first line of defense would be to have a white roof.  Even so, you may want to investigate a reflective product such as rFoil (one brand - http://www.rFOIL.com).  These products reflect radiate heat back to the outside, rather than allowing the heat to transfer inside.  It would be applied (stapled) to the rafters and would also provide you some minimal R-value for any heat convection.

1. 
   emerckx | Nov 24, 2003 09:11pm | #5

   Thanks for the help. Do you install it right against the sheathing, or do you leave an airspace? Radiant heat is the problem here, but we use insulation to keep the cool in and the heat out, too. Up north I think you would call it "wicked hot."

   Mike