Waterproofing rim board on shed roof
Doelman
| Posted in General Questions on
We have a rim board running along the ends of our eaves, should we waterproof them? We’re using rigid insulation on the roof deck, osb on top and below the insulation, high temp underlayment on top the entire roof, standing seam metal, and hardie siding for the fascia.
Seems to me we should go just ahead and run the underlayment to the bottom of the rim board for waterproofing. Thoughts?
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Replies
Doelman,
I look at them as part of the wall system. They need a WRB between them and the Cement board cladding, but you want the roof underlay to lap onto the finished fascia so that water can't run down in-between the two.
I’m not following, the exterior walls have a wrb (house wrap) but you don’t extend that to the fascia, it ends at the soffit. What kind of wrb would I use over the rim board?
Doelman,
The situation is analogous to a wall. You have a vulnerable material that will be clad, so it needs a WRB to protect it. You can use whatever you are using on the walls below, or for added protection a peel & stick membrane, as the rim boards (or rough fascias) can dry to the back.
Lap the WRB up onto the roof, then when you apply roof underlayment, lap it over the finished fascia several inches. The edge will get covered by the metal gable-trim.
That is a nice looking build!
For a metal roof with exterior rigid here is what I did.
The peel and stick was put over the main roof deck. This forms air and vapor barrier plus it gets the place water tight so the rigid and metal can go on later. Since the peel and stick is under the rigid, it doesn't need to be high temp so you also save a bit of cost.
The peel and stick ended at the facia boards, mostly so that if it even needs to be replaced, you don't have to deal with peel and stick.
Once the rigid was installed, it was covered by a synthetic underlayment (I like permeable one for this) and strapped out with horizontal 1x4s and metal roof was installed. The underlayment lapped over the facia board. Over this went the facia trim (metal color matched to the roof) and either a gable rake trim or eave trim.
Looking at your roof, make sure to figure out air barrier continuity around all those rafters. I think the simplest is to spray foam around the perimeter of the roof on the inside to seal from the top plate to the roof deck.