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nelsonC 01-07-2009 11:11 AM

venting metal roof for attic conversion
hi there,

our house is a 1932 bungalow. the roof is original, it's a standing seam metal roof over 1x12 sheathing (plenty of gaps between those old boards!). I do not think there is any venting (no soffits, no gable end vents, though there are windows on either end). currently, there is batt insulation between the decking and some old drywall.

we are beginning to think about converting the attic to a bedroom and the question of proper venting is first on my list. it's hot up there in the summer, and cold in the winter. I'd like to stabilize the environment a bit and make sure that I don't do any damage to the roof, decking, or rafters.

is venting necessary? is this the right approach? any info would be great, even if you can simply direct me to the right topic!


Tom Struble 01-07-2009 11:34 AM

can you see any tar paper thru the board spaces?

nelsonC 01-07-2009 11:37 AM

Good question :)

I'm not sure. I'm not at home right now to check.

What if 'yes' and what if 'no'?


nelsonC 01-27-2009 01:06 PM

yes, there is paper between the metal roof and the roof deck (which is made of 1x8 planks.

I should mention that there is a full-size window at one end of the attic, a door to a deck at the other end, and double hung windows in the dormer on the long side of the house. not sure if that factors into anything or not...


tinner666 01-28-2009 06:06 AM

I ddi a photo essay in the shop showing how to box the panels, wrap the wood blocks, install the dripedge. I didn't include the 'run and bend to lenght' metal ridge-cap that hooks on the drip-edge though. Hope this helps.

tinner666 01-28-2009 06:09 AM

1 Attachment(s)
A pic of the blocking in place, with the drip-edge on. No cap yet.

Tom Struble 01-28-2009 09:43 AM

i could look at pictures of your work all day Frank

nelsonC 01-28-2009 11:03 AM

thanks, and nice work there :)

but unfortunately, I think I need a little more background information on the topic.

a) is further venting necessary, beyond the inherent venting I already have by virtue of the current design and

b) if so, which method is preferable?


Tom Struble 01-28-2009 11:45 AM

it all depends on how much and what type of insulation your using.Trying to install a vented ridge on an existing metal roof requires a good deal of expertise as tinners photos suggest.Maybe spray foam insulation would be a better choice

nelsonC 01-28-2009 12:36 PM

ah, I see.

currently, there's fiberglass batt insulation. R-29 or something. but we'll be removing the current drywall from the "ceilings" and we'll probably be removing the fiberglass batts as well so we can inspect the roof decking from underneath.

everywhere else in the house, we've used UltraTouch denim/borate batts and since frankly, the fiberglass is a nasty product, I just assumed we'd replace the existing with the denim in the process.

I guess I'm still not sure how the roof would be vented (if it even needs to be). there are no soffits or anything. if we installed batts, would leaving a space between the decking and insulation be sufficient? is that necessary?

if using spray foam, would the same principles apply? that is, leave a gap?

I wonder if there is some venting already happening since the space between the decking and paper/metal is not truly air tight.

thanks for the information and you patience!


tinner666 01-28-2009 04:11 PM

Well, I'm no expert on insulation. Here's a link to 2 pictures of one attic that was closed off.

The 'float' between the wood and metal is not enough. You must provide 1-1/2" of airspace between the insulation and the underside of the deck.

To vent an existing tin roof;
1. I'd cut the roof on both sides, 1" from the ridge.
2. I'd stop about 18" from each end, valley, chimney, OR whatever.
3. I'd use tongs to bend metal end up 1" , continously. A little at a time please! It MUST be finessed to the 90 degree position.
4. Paint all your 3" wide, 1 1/2" tall blocks, cut to 1" less than the panels are wide.
5. Wrap the blocks with metal and paint them.
6. Screw them to the roof**** HERE"S WHERE IT GETS TRICKY!!!!!!!!!!!!!
You have to figure the size of the drip-edge that goes on the blocks, mainly it's overhang. You must lay blocks and a even a small piece of DE on opposing sides, and use 2 straight-edged rulers that cross each other at the NEW ridgre apex created by the blocks! The distance to figure will depend on your ridge metal; 20" wide metal, with both edges folded under to lock on the DE will probably be less than 9" on either side. So, the front edges of the blocks may be 5" to 7" down the roof from the original apex. You WANT the ridge to have 1/2" play, DE to DE, final dimension.
( I'm fully confused now, so I hope you were able to follow this!)
Bend the cap metal with tinner's tongs and over bend it a bit. You can fully bend one locking edge under to hook onto the DE, the other side only prebent to 90 degrees. Use your hands to start bending it into place, finish with the Malco S-3 hand tongs.

tinner666 01-28-2009 04:15 PM


Originally Posted by strublesiding@optonline.n (Post 220597)
i could look at pictures of your work all day Frank

:eek: Well, thanks. You're welcome. :)

Tom Struble 01-28-2009 09:36 PM

im not an insulation expert either but there are what are called hot roofs.Thickly sprayed foam insulation with no venting needed, its a specialty trade,maybe you can consult with a local spray foam contractor and get recommendations from him. Or hire tinner to vent your metal roof for you.Good luck

nelsonC 01-29-2009 07:05 AM

thanks for the replies, all. it seems like the best thing for me to do is hire someone to come have a look at the house and explain my options.

Tinner - by the way, I've now got your DIY site bookmarked. I'm in Nelson County, just over an hour down route 6 from you. we're just starting to plan this job (which also includes installing a dormer) and collecting a list of resources and information.

Sam Braidley 01-21-2010 02:32 AM

The original design for our house included gable vents. Those vents were blocked when my wife decided she wanted taller ceilings in two upstairs rooms. So, the builder added three or four non-powered attic vents to supplement the softy and ridge vents.
However, our roof is very large with a great deal of surface area and I have always believed it's a lot hotter in our attic than it needs to be. So, I'd like to add one or two powered attic vents--without cutting new holes, if possible.

Then after a long search on the internet i got the suggestion from a friend told, You can get the magnetic sheets like they use for the signs on the sides of work trucks, that would seal air flow from the interior". Now, I put that on my swamp cooler vents in the garage during the winter. Not as cheap as Styrofoam, but easy to install and remove. I stick it to the sides of the washer and dryer when not in use.

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