Frame shed roof over existing flat


#1

Hi all, I have a 12 X 14 screen porch addition with a flat roof tied into the house with a 10-in-12. I want to frame a shed roof right over the existing flat(leaking and in terrible shape) & tearout and re-install t&g interior ceiling. Couple judgement questions:
1)Should I bother tearing entire old roof off?
2)Want to go ahead and insulate ceiling ( may close in some day)whats the best way to vent shed roof?
3)want to match existing architectural (timberline) shingles - although I only wanted to frame 2 ft higher at roof intersections, thus making shed only a 2/12 -any suggestions?
Any input would be appreciated
j


#2

**
1)Should I bother tearing entire old roof off?**

By your own admission it is, “leaking and in terrible shape” so yeah…I’d rip it.

2)Want to go ahead and insulate ceiling ( may close in some day)whats the best way to vent shed roof?

Pictures please; it depends on how/where the dormer terminates, etc.

3)want to match existing architectural (timberline) shingles - although I only wanted to frame 2 ft higher at roof intersections, thus making shed only a 2/12 -any suggestions?

First, do you know how to figure pitch? Just because something is " 2ft higher" does not make it a 2/12.

Why match it (color), doubt you will be able to see such a low slope from the street. You could match it with peel and stick low slope material but it won’t have a warranty if it is under a 3/12. You have numerous low slope options but you’re taking a chance on compromising the job if you use a material that will match your current shingles. It can be done using these materials but IMO it should not be.


#3

[quote=“Tar Monkey”]**
1)Should I bother tearing entire old roof off?**

By your own admission it is, “leaking and in terrible shape” so yeah…I’d rip it.

2)Want to go ahead and insulate ceiling ( may close in some day)whats the best way to vent shed roof?

Pictures please; it depends on how/where the dormer terminates, etc.

3)want to match existing architectural (timberline) shingles - although I only wanted to frame 2 ft higher at roof intersections, thus making shed only a 2/12 -any suggestions?

First, do you know how to figure pitch? Just because something is " 2ft higher" does not make it a 2/12.

Why match it (color), doubt you will be able to see such a low slope from the street. You could match it with peel and stick low slope material but it won’t have a warranty if it is under a 3/12. You have numerous low slope options but you’re taking a chance on compromising the job if you use a material that will match your current shingles. It can be done using these materials but IMO it should not be.[/quote]

I’ll go one step further on the tear-off question, and ask the homeowner what they plan on doing if/when the new shed roof leaks and water accumulates on the flat roof until it can find away in. In the meantime, there will certainly be some mold growth, and maybe even some good old fashion deterioration of the wood framing and/or roof deck.

As for venting, you can vent along the ridge/head-lap where the roof ties into the house. You can also vent along the eave and/or soffit, depending on how you construct the thing.

If it really is 2:12 slope, be sure to install ice and water shield over the entire deck first, or at least double felt is with 30# felt before installing the roof if you plan on using shingles. If you can, you may want to use a modified bitumen that is the same color as your shingles. Although, I must say I’d try to get more slope if you can, or go back to a new low-sloped roof, as 2:12 is really kind of an area in between sloped and low-sloped roofing.

As for insulation, if you went with a new low-sloped roof you can insulate with the roofing. If you go shingles, I would install/apply a radiant barrier and would either insulate underside of roof deck or top of ceiling all depending on your ventilation, etc.


#4

to much question.

gweedo


#5

strip the roof,
pull some nails,
lift up the rafters
build a kneewall
fill in the space
voila…instant cathedral ceiling


#6

Ok I will clarify this a bit -
I was looking for peoples experience in terms of building a new roof over an existing roof. It is done & I have worked on many houses with this characteristic - just have not done it myself. I am interested in pros vs. cons (mold, ventalation, insulation, ect…)

Cerberus Wrote: “I’ll go one step further on the tear-off question, and ask the homeowner what they plan on doing if/when the new shed roof leaks and water accumulates on the flat roof until it can find away in”.
I do not plan on building a roof that will leak. THat is why I am asking for advice on matching the architectural shingle look - which is the desire of the homeowner. - I know pitch & reveil is more of an issue with this type of shingle…So, as a framer, was wondering from a roofers standpoint what my options are. I can raise the rafters higher up the roof of the house, and increase the pitch. But homeowner wanted to keep it lower and less intrusive if possible. ???


#7

Building a “false deck” is kind of cheesy but I have done it before to raise the pitch of a roof.

If you have control over the pitch then make it a 3/12. Now you can use GAF Liberty or Certainteed Flintastic peel and stick low slope systems and it will have a manufacturers warranty. I think the Flintastic is a bit better as far as color choices but either system is a good choice for both ease of installation and matching existing shingle colors.

You can also do a 3-ply torch app on the existing roof after it is stripped and then build a “false deck” over that sitting it on sleepers and then you can shingle the top deck.

You can also Ice and Water barrier the deck and toss down double coverage felt and shingle over that.

Making the new deck a 3/12" is your safest bet though IMO.


#8

Thanks for the input - upon further research and estimating I’m not so sure this is the best option. Not sure what a new roof will cost on this 12 X 14 flat roof - but probably cheaper than my estimate to tearoff, frame shed dormer,deck,ice guard, shingle, new fascia, soffit…
I appreciate your responses.
regards,