Worried about added weight on roof redo


Hello, any help would be greatly appreciated. I am preparing to reroof my house. I’m a little worried about the weight I will be adding.

Here is the current roof: 2/12 pitch. Cathedral ceiling with 18ft span from outer wall to wall running down the center of the house. 2x6 t&g decking sitting on 3.5" x 11 1/4" beams on 6ft centers. 1" beadboard insulation, 7/16" osb. shingles.

I would like to tear off the roof down to the 2x6 t&g, then add:
15lb felt
6in polyisocyanurate insulation
A “ventilation panel” made of 7/16" osb, 2x6 blocks as spacers, and 5/8" plywood (weight of one 4x8ft panel is 110 lbs.
Malarkey 401 self-adhered underlayment
15lb felt
Malarkey legacy shingles (275lbs/square)

The difference then in weight is that the panel adds perhaps 70lbs/32 sq ft, the shingles are heavier, I have 2 more layers of felt/underlayment than currently, and the insulation adds something (negligible surely) I would guess that the sum added weight would be on the order of 3 lbs/sq ft then.

I live in southeast Colorado. Snows can be substantial but we aren’t in the mountains.

In addition to comments on this additional weight, I’d welcome any comments on my overall roofing plan.





Will not comment on the weight issue. You need an engineer to figure that out.

On a 2/12 why are you going to use shingles? I would use a single ply system.


Ditto Lefty


The house has a steeper pitched front roof that is already roofed with shingles to answer the shingle question. I am tying into that roof. Malarkey will warrant the 2/12 roof as I am planning to roof. Let me ask the original question another way. Any idea what the dead load bearing requirements for a roof are?


Well…I like Malarkeys.As far as your concerns on weight issues,you need someone qualified such as an engineer as Lefty stated to answer these questions.


No doubt you should consult an engineer. I do it all the time with remodeling projects. For just a few hundred bucks, you can get him to tell you it’s ok or what you need to do to make it ok. the beauty of it is if he is wrong its his liability not yours. so when the roof caves in his insurance will pay

Also you’ll be ok with shingles-water & ice all the way up


Why not metal?


Im not a big fan of I&W on the entire roof. If the roof is done right that should not come into play.I do not agree with shingles arch or dimensionals being put on that shallow of a pitch, They will warranty the shingle not its ability to shed water so please do not be mis-guided and thats if its installed correctly. A shingle weighing 275 a square sure not a 3 tab. Either way a single ply or atleast a peal and stick should be used if you want years of service from the roof. All that I&W will just mask the leaks IMO. Lefty knows what hes talking about He has encountered many problems and found ways to fix them.

As far as the weight issue you need to hire an engineer for that. Too many things we can not see, i dont understand the 6 foot on center thing thats impossible no code would allow that.



I would not put the shingles on the 2/12. Use a single ply there.

Ice and Water shield will be your roof system. The shingles will be there for appearance only.


You said it better lefty.


did i read 6 inch iso? is this bldg a freezer? use a single ply like lefty suggested!


somethin tells me go up there and jump up and down
on the roof inbetween rafter beams and if the roof kinda bounces a little to much, and doesnt feel that strong, then i would put on just what i need to put up there.
if it doesnt move and feels very strong, as most t&g decks are, then ad some weight.



I don’t know who you have been talking to but you should forget your entire plan. tear it off and put a tpo or pvc roof system on then you can use your poly the way it is meant to be used. I roof in Jackson Hole WY, Big Sky MT, and Island Park ID wich have some of the heaviest snow loads live or dead in the nation and I would not put that much weight on anything that was not specifically engineered for your system. I would be concerned for my company and the safety of others. If you are dead set on shingling it cut down to a 30 year highlander cs and use one layer of high temp Ice and Water shield on top of 2by sleepers full of spray foam insulation to achieve a high R value. This will cut down on the weight and give you a conditiond roof. Be carefull this sounds like a job for a pro.