A choice; rain screen or extra insulation? There’s not room for both…
Greetings. I am finalizing the design of my exterior renovations and have a dilemma. I am planning to install new windows and trim them with 2×6 red cedar casings. The thicker trim will allow me to add a layer behind the new red cedar shingles that I’m installing. I can add up to a half inch of material behind the shingles before the siding is flush with the face of the trim. I am considering what to do with this space and have narrowed it down to either installing a rain screen or some rigid foam. I don’t have room for both, so I thought I’d ask this forum for some opinions. Which should I choose? Now for some details: 1. The walls are 2×4 construction with batt insulation. 2. Budget allowing I will replace the batts with spray foam for better r value. 3. My home is in the northeast. South-central Connecticut to be precise. 4. I can see the coastline from my home but am about 300 yards from it. Any input you have on this decision is much appreciated. Thank you in advance. Peter
Replies
Rain screen
Half an inch of foam isn't enough to do much, and might actually cause problems unless you make it thicker.
Choice
I'm in agreement with David. I think the rainscreen would be a better investment.
Not sure what you mean by rain screen.
If you mean a WRB (weather resistant barrier) like Tyvek, it's thickness is negligible, but if applied right, it will shed bulk water, stop air movement, and still allow the wall to dry to the outside. And drying to the outside is probably important in your case, especially if the inside of the walls is not very carefully and fully vapor-sealed to prevent moisture transfer from the inside during the heating season. Your cedar shingles will do a good job of allowing drying to the outside.
However, if you install sheets of rigid foam under the shingles, you will be preventing drying, since the foam will act as a vapor barrier to moisture that originates on the inside.
Proper installation of a WRB along with other good air-sealing measures will give you more benefit for their cost than anything else you can do.
And, to me, the trim looks much better if it stands a half-inch proud of the shingles.
not sure what rain screen means?
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http://search.aol.com/aol/imageDetails?s_it=imageDetails&q=rain+screen&v_t=keyword_rollover&b=image%3Fquery%3Drain%2Bscreen%26s_it%3Dkeyword_rollover%26oreq%3D53c584dbd1e54404b0efc26420e2768e&img=http%3A%2F%2Fwww.coastalcontractor.net%2Fimages%2Farticles%2F2007%2F0703%2Fcoa0703_fig7.jpg&host=http%3A%2F%2Fwww.coastalcontractor.net%2Farticle%2F135.html&width=126&height=72&thumbUrl=http%3A%2F%2Fimages-partners-tbn.google.com%2Fimages%3Fq%3Dtbn%3AANd9GcRtGAJPPMkBS9UuY2ReiSSCAj0AecKnZBSs3XZqqffmLfXb0cjd9rFxRw&imgWidth=450&imgHeight=256&imgSize=17068&imgTitle=rain+screen
My apologies for these huge links.
If someone wants to Tiny url this, be my guest.
thanks.
Use thicker window trim or an alternate method of installing it, and do both the insulation and the rainscreen. The additional cost will be minor and the benefit huge.
Exactly... The siding comes off the wall once every 25-50 years... but you pay for heat EVERY year, and it's never any cheaper the next year.
Do the RIGHT thing, not the EASY thing.
That's news to me. Most siding I see here has been on for 60-100 years
Yah, you should really do something about that. Having to replace siding every 25 years ensures there are people who know how to do it... 60 to 100 years means there are alot of youngings goin "What the heck is the "Siding" you speak of?"
You need to do a worse job on your siding details so someone else will know how to fix it.
Sorry - was that coffee you just blew alo over your monitor?
Got some on you, did I?
Hmm thicker trim. I'm already sizing up to 2 by 6..
I wonder if red cedar trim boards thicker than 2x6 are readily available at a reasonable cost. The idea of both foam and a rain screen such as home slicker is appealing but I'm dubious that I can find lumber this thick. Perhaps I can fur out the 2x6 casings additionally but that would add complexity. I like the KISS approach, keep it simple, stupid.
Only the part you can see needs to be cedar. Put pine or whatnot under the cedar trim.
Thicker foam is a good idea
but you don't need thicker trim, you install the windows and the trim on top of the foam instead, so the trim details are normal. On the inside you have a deeper extension jamb.
Interesting thought. The only times I have seen thick foam installed beneath shingles are with a sip-type scenario wherein the foam has a layer of osb or plywood over it. That kind of sandwich construction sounds costly but perhaps there is another way. I was hoping to simply nail the shingles thru the half inch foam much like vinyl siding is installed. I know a half inch doesn't give me much, but there is the added advantage of the thermal break. Can anyone suggest where I might find some details about foam exterior applications with flashing and window details? Thank you all for your replies thus far. Peter
Start here:
http://www.greenbuildingadvisor.com/blogs/dept/musings/how-install-rigid-foam-sheathing
Notice that the article is full of links to related articles. Read as many as you can stand...
I don't understand why you don't have room for both.
Install the foam put tnhbe windows in over it, then do you rrainscreen.
Alternatively, use a housewrap like GreenGaurd or the Typar with wicking action over the foam