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How to frame a roof with exposed rafters

1110d's picture

I'm trying to figure out how to frame a roof where there are exposed rafters.  Short of using SIP panels, I can't figure out how to insulate the roof.

Can't you just photoshop some (post #204936, reply #1 of 10)

Can't you just photoshop some compromising pictures with a prostitute?

(Though what you want to do is unnatural, so maybe they should be pictures with a goat.)

One way or another you have to fake it.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

SIPS are the quick and easy (post #204936, reply #2 of 10)

SIPS are the quick and easy solution to that - think long and hard about why you WOULDN'T use them.

I am redoing my own roof at the moment, and one part I'm doing is similar to what you want to do.

The rafters are not exposed in my case, I'm just going over the existing rafters for insulation value.  I'm leaving the existing 2x6 rafters and 1x6 cedar deck boards on the roof.  Over that, I'm putting on a layer of TYPAR.  Over that, I'm furring Up with 2x10 boards - they are not structural, other than carring their own weight down to the existing rafters.  Over that I'm putting the exterior deck.  Inside the furring rafters I'm putting in foam board air channels for eave to ridge vent air flow, and under that is going to be filled with cellulose.  This assembly gets to about R30 which is an Energy Star roof in my area (it also will have white shingles).

I only have to do that with a couple small sections of my roof.  If I had to do the whole thing, it would be MUUUUCH easier to lay a 6" SIP over the whole thing.

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If there are exposed rafters (post #204936, reply #3 of 10)

If there are exposed rafters there, it is already framed.

 

Foam over, then sheathing with long structural screws, or the SIPs

 

 

Oh Well,

We did the best we could...

This gets me to wondering... (post #204936, reply #4 of 10)

This gets me to wondering... for adding on a thick layer of foam for insulation, is SIPS cheaper than rigid foam sheets?

Using this guy as the hypothetical example, here are the two options laid out:

RIDGID FOAM BOARD

Over the exposed rafter beams, the exposed deck is placed - say T&G plywood.  

Over this, individual 4x8 sheets of 4" foam are placed, with vertical 2x4s on the flat screwed through to the rafters to act as nailers.  Gaps between nailers filled with 1.5" foam sheet.  Seams are foamed and taped.  OSB deck attached to nailers, then covered with roofing choice (felt & shingles, whatever)

This option can be done with a crew of carpenters, speciall attention to sealing all the seams in the foam.

<-vs.->

SIPS

Over the exposed rafter beams, the exposed deck is placed - say T&G plywood.  

Over this deck, 4' x 20' slabs of SIPS are craned onto the deck.  Crew takes care to screw SIPS down to rafters.  Seams are foamed and taped.  SIPS deck is then covered with roofing choice (felt & shingles, whatever).

This option requires a crane and specialized crew, but can potentially go on much faster with fewer seams to detail.

 

Based on your experience, is there any clear advantage you see to either method?

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You wouldn't have to sheet the rafters b/4 SIPs (post #204936, reply #5 of 10)

The panels can be spec's with a covering of choice.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


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I have not used SIPs here on (post #204936, reply #6 of 10)

I have not used SIPs here on the island. No crane. Tho it is possible given a large enough job. Did not know you could get better finish details on SIPS interiors. Often, with exposed rafters, a T&G V-groove or beaded board is the desired ceiling.

 

But to Paul's Q, Labor savings with SIPs would generally dominate for a larger job. Also, speed of enclosing space against weather has a definite value

 

 

Oh Well,

We did the best we could...

A V groove plywood panel (post #204936, reply #7 of 10)

A V groove plywood panel isn't going to look as good as T&G pine on stained exposed underside, if that is what's intended.

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____________________________________________________

Whatever you say Paul. (post #204936, reply #10 of 10)

Over the exposed rafter beams, the exposed deck is placed - say T&G plywood. 

Well, I replied to the statement above-if you want plywood, you can have it on the SIP panel. 

If you are first installing boards on top of the rafters, then you still could have plywood on the SIP panel-gives some nailng base once installed (if necessary).  Or OSB, or Drywall................

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/

 


Rafter tails and insulation. (post #204936, reply #8 of 10)

If you are looking to retain the "exposed rafter tail look", but you want to add insulation, then you really have two different situations. First, the easy way would be to use SIP's or layers of XPS added on top of the existing roof followed by sheathing and shingles (or metal). But think about that for a minute.................your rafter tails would have a truelly UGLY layer above them (the thickness of the insulation) that you would then have to finish off with a new facia, etc.

A better looking approach that we have used on many bungalows (new construction and rehabs) would be to add the insulation above the existing roof (usually XPS sheets) and add "Faux" rafter tails that we usually construct from cedar 2x8's that we add onto the side of the roof to match the insulation height. In essence we have moved the tails up. That way you still have the sleek look of the tails.........kinda looks like an "uninsulated" roof, but you have all the insulation you need!!!

I assume that's what you are seeking.

Of course, if you have full access from the inside, just sprayfoam between the ceiling joists.

Bob

But he said exposed raftes, (post #204936, reply #9 of 10)

But he said exposed raftes, not just rafter tails

 

 

Oh Well,

We did the best we could...