Replies

1. 
   xxPaulCPxx | Sep 06, 2011 11:42am | #1

   That foil faced foam board will act as the water barrier - no need for the tyvec under it as long as you taper the joints well.

   Why are you only using 1/2"?  You get a TON of bang for the buck by adding foam to the outside of your walls, it doesn't make much sense to do all that work and only add 1/2" of insulation.  Unless you live near me in SoCal, where it's about 70 year round.

   As far as the radient barrier details - look at attaching vertical furring as nailers for the siding.  This sets up the air channel needed for the radient barrier to work - it's also called a "Rain screen" which is the other benifit of this method.

1. 
   hchattaway | Sep 06, 2011 06:45pm | #2

   Foil faced insulation

   Thanks Paul for the reply...

   Good point about the Tyvec not being needed... makes sense to me.

   But the furring strips are really still needed? With the foam board, that doens't serve the same purpose as the air gap for preventing the heat from getting to the house? I live in North Central Massachusetts BTW... 

   The house is a ranch 40 ft x 26 ft. Pretty small.. with the other insulation and new windows I've done  I can go a heating season on a litle over one tank of oil... not bad this far north!  Looking to improve more with the foam panels...

   I'll look into getting the thicker foam panels.. still on order with Lowes...I can still change it..

   Thanks

   Harold

1. 
   DanH | Sep 06, 2011 07:16pm | #3

   You need a physical air gap (or a layer of IR-transparent glass) for the radiant barrier to work.  On the outside you'd get that, more or less, from the vinyl siding, but the inside foil layer would be ineffective if it had no gap.

1. 
   hchattaway | Sep 06, 2011 11:09pm | #4

   Order...

   Hi Dan...

   So the order would be, house, furring strips (to create gap), rigid insulation sheets with radiant barrier, then vinyl siding? The gap under the vinyl siding being ok for the outward facing radiant barrier?

   Thanks

   Harold

1. 
   DanH | Sep 07, 2011 06:57am | #5

   The gap under the vinyl is less than ideal, but would serve the function.

   But don't get hung up on the whole radiant barrier thing -- it's effectiveness in this situation is not apt to be substantial.

2. 
   mike_guertin | Sep 07, 2011 03:26pm | #6

   In MA - Thicker foam=good, radiant barrier on wall=not effective

   In general, radiant barriers aren't going to give you much bang for the buck in northern climes especially on the walls.  The story changes as you move south but in MA - don't give it a second thought.  

   Regular lap style vinyl siding drains pretty well even without being furred off the drain plane.  First, vinyl doesn't absorb and hold moisture (like Fibercement, wood or brick) plus the proper install method of hanging vinyl leaves the hem free of direct contact with the weather resistive barrier so water can drip freely through.  Then there's the natural spaces behind most of the panels - good capilary break and pretty decent airflow for drying to take place.  See third parragraph here -  http://www.buildingscience.com/documents/reports/rr-9909-drainage-planes-and-air-spaces for more info.

   Foil faced insulation is fine to use; just don't sweat the radiant benefit or further details to increase the airspace between siding and the insulation.

   Do however consider PaulCP's suggestion to go for thicker insulation.  You're only going to get one chance to add insulation board on the outside.  I usually go for at least 1 in. polyiso and would nail vinyl through it.  Thicker is better but use screws for insulation greater than 1 in. thick to minimize hems dropping.

   MG

1. 
   hchattaway | Sep 08, 2011 09:10am | #7

   Agree with thicker foam...

   Hi MG,

   I can definitly see your points about the insulation.. and will adjust my order of foam... Lowes ordered way too much of it anyway when i went over the receipt, I noticed it!

   Thanks

   Harold