Second Roof?

Hi Guys, need you advice on this idea.

We've finished the north side, with 1/2 plywood and under layment.

The problem is the ice dams will still occur.

1) Close ceiling
2) Only R30 in slope roof/ceiling
3) Extreme winters, ice rain
4) History of icedams

As it is now the heat will go through the roof and melt snow and ice and create ice dams then force it's way in the house eventually. Maybe i'm wrong but i imagine it won't last very long...

Sure the ice and water shield will help but the only way i can think to solve the problem is a second roof.
It would take about 1 day of labour. Use 3/8 osb, a sheathing 2x2's Probably only cost $500 but cheap insurance on a 5k job. In the future 10-20 year the whole thing would just be pulled off and replaced with new shingles and osb. I would just sheath all on the edge.
It is a sort of insulation that 1.5" gap. It will keep the mass of ice and snow out of the house.

Should i spend the extra money and time now? The other side is already done, so can't take that off.

it would be better overall to fix the problem.
install ice/water shield to code for your area
ensure proper ventilation and balance (i.e.- too much ridge vent, not enough soffit venting, insulation over soffits, etc...)
install adequate attic insulation for your area.
you'll save on energy costs and water damage at the same time

That's the trade off of having a cathedral ceiling, close ceiling. More space less efficient. A second roof would increase r -value efficacy by making the roof drier and colder.

The hidden roof (野屋根 noyane?)[note 1] is a type of roof widely used in Japan both at Buddhist temples and Shinto shrines. It is composed of a true roof above and a second roof beneath,[1] permitting an outer roof of steep pitch to have eaves of shallow pitch, jutting widely from the walls but without overhanging them.[

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Your double roof is what quite a few people are doing around here. I don’t know if it’s right or wrong and the Amish seemed to be the ones starting it around here. They are stepping out from the old shingle roof without removing it with 2x4’s running back and forth that also act like a ladder for climbing the roof then they put pole barn painted tin roofing on. The air gap seems to help with getting the snow off along with the smooth tin. They look ok now that folks are getting used to seeing them and they seem to hold up a long time.

There are also a lot of people that say leaving the shingles on is stupid and to take them off to check the sheeting etc. and then roofing paper then strips and then tin. I personally don’t like all the horizontal strips under the tin and poking all those screws into the old roof. Seems like any water getting past the tin will get guttered by the strips and find the holes.

There are also people putting the tin right to the shingles and say the smooth tin and the ridges alone without the space do the job.

The other thing I don’t like is how they handle the flashings. Every one doing it seems to have a different method and they all require a lot of goop.

There are a lot of poor people around here that can’t afford much and they have a roof falling in and in a weekend a few friends or the Amish can throw one of these on. I used to see them up there coating the shingles with roof coat.

The trapped air space will allow for moisture to collect on the back side of the metal creating a perfect environment for organic growth.

Bud brings up several great points and remember, just because someone does things, does not mean they are a good value and won't create another set of problems down the road. Buyer beware.

When I questioned them on the airflow the answer I get is the ribs in the tin allow the air flow to the ridge even though the 2x4 run the wrong way.

I would think a better method would be running them up and down to make the air space but then you would have to figure out how to attach the second roof.

Maybe someone makes a system that works and solves all the problems of a double roof system?

bud16415 said:

When I questioned them on the airflow the answer I get is the ribs in the tin allow the air flow to the ridge even though the 2x4 run the wrong way.

I would think a better method would be running them up and down to make the air space but then you would have to figure out how to attach the second roof.

Maybe someone makes a system that works and solves all the problems of a double roof system?

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They stagger the 2x4s to allow air flow

nealtw said:

They stagger the 2x4s to allow air flow

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Staggering the 2x's will inhibit airflow and the real problem is condensation on the underside of the metal panel. Metal MFG's want the panels flat on a hard surface with no air space. Installing over existing shingles creates another set of problems. The old shingles will continue to deteriorate, cup, curl and lift the fasteners out of the roof deck.

oldognewtrick said:

Staggering the 2x's will inhibit airflow and the real problem is condensation on the underside of the metal panel. Metal MFG's want the panels flat on a hard surface with no air space. Installing over existing shingles creates another set of problems. The old shingles will continue to deteriorate, cup, curl and lift the fasteners out of the roof deck.

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Agreed, Jungle should have done this before he put the new sheeting on or better would have been to sister the rafters for better venting.
In fact when a second roof is added the inspectors want holes cut in the first one, go figure.

Roof over a roof and you end up with a double vapor barrier. And another set of problems. If he would just cover the whole roof with Ice and Water shield, problem solved.

I think the problem is even though i have dura vents in the rafters and 2 layers of roxual and ridge vent is still the decking will be too hot. My roofer guy thinks the heat will just go through the roof and melt everything.
I did put a lot of ice and water shield. Probably not enough bellow the skylights because neil nor the roofer guy did not advice me in time of this.

But we did use a fair amount. I used a good quality synthetic underlay so i am optimistic that water from the ice damns will not penetrate.

I think if i make a foam insert to fill the skylights it may solve problems in the winter. Mind you the extra light is GREAT and i am sure in the winter it will be even more important.

Ran out of time and patience for the second roof idea but i do believe this is cheaper alternative to a metal roof. With cheap OSB and 2x2 sheathing the roof and SHINGLES would have not cost that much more and much less than even standing metal (good metal roofing cost $4+ a sq BTW)

This will keep the ICE and SNOW off of the house. In other words not attached. The decking being so close is almost part of interior house. So the cold and damp of the ice and snow will transfer into the house by convection i think. Oh well. I could have use another layer of roxual might have help, maybe not. I think the heating would still be going most of the time in winter. That layer would cost an extra $1200.
The total cost i just work out for the roofing job (it's about finished now.) Including 2 skylights and mix up of reinstalling them was about $2000 for labour and whopping $4000 on materials, dumpage and tools rentals. I worked the same hours and more so add another $2000 for me. So that is at least 6k-8k for DIY job. So how much would a pro roofing company have charged me? Is it fair to say this would be a least 10k job? I had no idea it would be this expensive.
I think it is well done job, the roofer guys has many years of experience. The new decking was air nailed with so many nails it could survive a Florida hurricane. If it wasn't for removing the old decking the job would have cost much much less.

Go back to when you were working on the inside, I will bet that I suggested makeing the rafters 10 inches deep so would get proper ventilation.

I know i expect a lot from internet eh. I said the same thing to the roofer guy, why didn't you scream it if you know you are right? It is like on a ship - when it sinks we are all dead!

It is my responsibility so ultimately i make the decision and take the blame and cost when it is done incorrectly. I know plenty of 'contractors' that would have done a much cheaper and poorer job. Cuz who wants to pay 12k for a new roof?
I grew helping my dad build cottages but then did other things for many years, if i didn't have a university degree there would be no way i'd be here now. I like trying new things, even if it fails because you learn much more that way.