# How Do Vent a Finished Attic?>



## RackCityRoofer (Jan 31, 2012)

house has a finished attic.
1shingles 2roof deck 3insulation 4drywall


how does the air move from the soffit to the ridge
if the rafters are 2x4 that leaves 3 1/2 in stuffed with insulation?
how can air move up and out......
how do i vent?
thanks RackCityRoofer


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## Interloc (Apr 6, 2009)

Either shoots up between rafters or a build up rafters..is this a reroof??


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## shazapple (Dec 3, 2010)

If this is a re-roof I would remove the existing roof down the deck, place 2x4 strapping over the existing deck, new sheathing over 2x2's, and then new felt and shingles. Optionally you could install a layer of rigid foam insulation between the exiting deck and strapping.

I would check to ensure the roof joists are actually 2x4. Seems a bit low...


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## vtroofing (Sep 27, 2009)

Many homes were built with rough sawn 2x4 rafters either on a steep roof/ cape style whereas the span (s) are short- maybe plate up to knee-wall up to collars/ ceiling joists and then to ridge. 

These are always bears when on a finished interior space providing adequate venting and/ or insulating. 


Your question was how to vent the attic. Well on a Roofer's Forum, we should all jump on the replace roof add insulation and ventilation by going up, however if the roof is not near replacement time it seems like it would be the most expensive. 

Accessing just the slants by removing drywall/ lathe and plaster and either building down and create the needed air space by installing:

1. Proper vents for batt insulation, with additional 2x attached to underside of rafters to create enough depth.

Alternatively Spray Foam which has gained a ton of retrofit work such as this will need solid substrate to keep airflow. 

2. 2x2 cleats pushed up against the bottom of decking, install hard substrate OSB or plywood and then spray foam. In this scenario additional 2x's will need to be attached to underside of rafters as well- although much- less as Spray Foam has greater insulating capabilities to. 


***Open-cell SPF has an R-value around 3.5 per inch and typically uses water as the blowing agent. 

***Closed-cell SPF has an R-value of around 6.0 per inch (aged R-value) and uses high R-value blowing agents.


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## Grumpy (Oct 29, 2008)

Either build up a false roof deck or use Atlast ventilated nail base. The Atlas product is nothing more than a factory made false roof deck.


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## 4 seasons (Dec 31, 2009)

I agree to do a built up roof, depending on the size of the roof it may be the most cost efficient option.


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## O'Donnell Roofing & Solar (Jan 17, 2011)

Adding another layer of 2x2 plus CDX may have a load problem.
A structural engineer should be involved.

How about when the roof is off, removing select sections of the deck and slide the baffles (rafter-mate) in between the insulation and roof deck.
Make sure the eves are vented

This should allow for air to flow up to the ridge vent.


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## vtroofing (Sep 27, 2009)

This is an old post. I am surprised the OP has not come back on and answered the questions asked. 

Is it time for a roof replacement?


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## shazapple (Dec 3, 2010)

O'Donnell Roofing & Solar said:


> Adding another layer of 2x2 plus CDX may have a load problem.
> A structural engineer should be involved.
> 
> How about when the roof is off, removing select sections of the deck and slide the baffles (rafter-mate) in between the insulation and roof deck.
> ...


Agreed, the weight should be looked at. I think stuffing baffles into the existing rafter space is somewhat counter productive, as it would reduce your R value by crushing the insulation. In the OP's case there would barely be 2" of space for insulation.


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## Merge (Oct 22, 2015)

check the roof joints


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