# building a new roof over an existing roof



## Runestone (Jan 7, 2007)

Our house has a hip roof. The shingles will need replacing in the next couple of years and the roof sheathing is not all that great in some places. Since we are planning an addition this year. We both agree that the whole house will look much better if we change the roof line from the hip roof to a sloped (pitched) roof. 
We do not want to remove the existing roof so we are proposing to build directly over the old roof. The new roof will be a metal roof. We are doing all the work ourselves so tearing off the old roof would be a real problem. I have finally confirmed that 'it's allowed' in Ontario provided the plan passes the building inspector. [Yippee, the NEXT hurdle]
So, I'm curious - Has anyone done this?


----------



## fordson major (Jul 12, 2003)

we have gotten plans passed by building inspectors, have had to go to engineered drawings. depends on the jurisdiction you are in, our small rural township was incorporated into the city and now need engineered plans for every thing! have seen some reroofs over top of the old roof you would be best to talk too a truss company about their take on your project. our neighbor did redo a hip into a pitch roof but removed the old roof before adding new trusses and a knee wall to add head room. if the wood deck is rotten then best to get it away from your structure.


----------



## MaryNY (Oct 25, 2004)

I suspect the weight of the reconformed roof with the existing hip roof under it would be more (possibly a lot more) than the current roof weight. If so, your wall studs and foundation may not be strong enough to take all that weight (think snow load!), and you at least ought to get some code enforcement officer or architect or engineer to figure it out for you. If you take off the old re-roof and reconfigure it, it may be close enough to the same weight that the structural strength of the rest of the house may not become an issue.

You also have to take into consideration that not only would a double roof weigh twice as much, BUT you will also have snow piled up on that roof for several months out of the year and if the snow load gets too great, you could have roof failure because of it.

Good luck!

MaryNY


----------



## JayinCT (Jan 31, 2003)

My guess would be changing over to a pitched metal roof would be more likely to cut down on standing snow load rather than increase it. I agree the weight of the additional roof over the existing roof should be considered, but a pitched metal roof does a great job of shedding snow and ice, just don't be standing under it when the slab let's loose!

Jay


----------



## Hoop (Jan 1, 2003)

One of my neighbors went from a hip roof to a pitched roof 2 years ago. This was a major project. Maybe a 3500 square foot house. In addition to changing the roof structure, they added on 2 rooms, added skylights, etc. I would estimate it was a $50,000+ project. He didn't even get a building permit......which in itself was a warning.

All I can say is, seek advice from a seasoned carpenter regarding structural aspects, logistics, plan of attack, prior to starting.

My neighbor was horrendously inept, insisted everything had to be screwed, used some godawful rough cut lumber, used cheap materials, and the method in which he undertook the project resulted in 3 times the labor.

All his friends/neighbors that were providing gratis labor quickly "found other things to do", and the guy was left stranded with a non-completed project. Summer has nearing an end.....fall & winter were on the horizon. He had to hire out a semi-retired carpenter, who grudgingly came to his rescue.

All I can say is this. It is so much easier to do things the right way.


----------



## TNHermit (Jul 14, 2005)

Take off the old roof and put up what you want. Your asking for all kinds of problems besides the fire hazard you have when you put one roof over another. They can't get into fight it. You have to tear part of it off anyway to set the new rafters on the plates. You can cut the rafters at the plate and have a crane come in and lift it off. I use to build the roofs on the ground and set them that way. (I have video) Cost me 200.00 to set so 1000.00 should cover a crane nowdays. Or a good carpenter should be able to use some of the old rafters and blend them into the new roof if its a hip and not a mansard type. some pics would be helpful.


----------



## Sand Flat Bob (Feb 1, 2007)

TNHermit said:


> Take off the old roof and put up what you want. Your asking for all kinds of problems besides the fire hazard you have when you put one roof over another. They can't get into fight it. You have to tear part of it off anyway to set the new rafters on the plates. You can cut the rafters at the plate and have a crane come in and lift it off. I use to build the roofs on the ground and set them that way. (I have video) Cost me 200.00 to set so 1000.00 should cover a crane nowdays. Or a good carpenter should be able to use some of the old rafters and blend them into the new roof if its a hip and not a mansard type. some pics would be helpful.


I totally agree, remove old roof and do it right. Have known of several attempts to cover an old roof with a new one, and it creates all kinds of problems. Best to salvage as much structural lumber from the old roof and build it right. One of my neighbors just changed the pitch and span of his roof. Carpenter did a great job and reused practically all the existing lumber. 

Good luck,

Bob


----------



## Beeman (Dec 29, 2002)

Runestone said:


> Our house has a hip roof. The shingles will need replacing in the next couple of years and the roof sheathing is not all that great in some places. Since we are planning an addition this year. We both agree that the whole house will look much better if we change the roof line from the hip roof to a sloped (pitched) roof.
> We do not want to remove the existing roof so we are proposing to build directly over the old roof. The new roof will be a metal roof. We are doing all the work ourselves so tearing off the old roof would be a real problem. I have finally confirmed that 'it's allowed' in Ontario provided the plan passes the building inspector. [Yippee, the NEXT hurdle]
> So, I'm curious - Has anyone done this?


 Need some clarification. Are you talking about framing a whole new roof, rafters and all over the top of your existing roof? Or are you talking about covering the shingle roof with metal and just eliminating the "hips" when you add your addition?

I don't know your area well, hip roofs supposedly have an advantage in high wind areas.


----------



## Runestone (Jan 7, 2007)

We are planning to frame the new roof over the existing roof. We aren't planning on going 'up' a floor so the roof would only be marginally higher than it is now. DH is a very skilled carpenter and is confident that he can do this work. The roof sheathing on the old roof is not rotten, just not up to the standards my DH thinks it should be.


----------



## Macybaby (Jun 16, 2006)

We put a "cold roof" over our existing roof. This section is 1.5 story. We laid the 2*4's flat, so this gave us a 1.5" gap for airflow. There were enough spaces between the old sheathing (1*8 boards) to allow airflow into the attic space. We also increased the overhangs and changed the soffits - it has no eave venting prior to this. Of course, we removed two layers of shingles and one of shakes before we put down the new framing.



















We'll eventually extend the lower roofline to create a porch in the front.

Here is what the upstars looked like after we got all the old stuff cleaned out.










We didn't change the roofline. You don't mention the pitch, or if you have any use in the area above your roof. If it's just attic, then you only need to worry about proper venting of the new ends. Cut a few holes from the old attic to the new attic.

Our house has several "roofs over roofs" as it has been added on to five times (at least). Usually this just meant going from the peak to a new support wall. Changed the pitch from 12/12 to 4/12. The old roofs (shingles over shakes) are still there, I sure wish the previous owners would have opened them up and only left the rafters.

This picture is taken from the laudry room (that once was an added porch). 









The wall use to be an exteior wall, and you can see the old roof in the attic. It's that way over the east den also. Our attic is quite interesting . . . We have access panels in several places as it's so hard to crawl from one end to the other.


BTW - we started working on the house fall of 2004. We should have everything done but the new kitchen cabinets by this summer.

Cathy


----------



## Beeman (Dec 29, 2002)

Runestone said:


> We are planning to frame the new roof over the existing roof. We aren't planning on going 'up' a floor so the roof would only be marginally higher than it is now. DH is a very skilled carpenter and is confident that he can do this work. The roof sheathing on the old roof is not rotten, just not up to the standards my DH thinks it should be.


 I don't know how much of a new roof he's planning on building. I think stripping the roof with wood like Macybaby did would give you added air space and plenty of support for a metal roof which is actually sheathing in itself. This would give you an air space under the metal which is what you want and give you a support grid for the metal.


----------



## Runestone (Jan 7, 2007)

If this worked, this is a picture of the house now. The new roof would go overtop and extend out about 12-14 feet for the addition. The addition will have our new masonry fireplace which means no more electric heat 

ETA - the addition will be on the south side (which is the left side of this picture)


----------



## TNHermit (Jul 14, 2005)

Sounds like you pretty well mad up your mind. But thats a little bitty roof. Ifin it were mine I would build the addition and roof it over to the house. Tear off the shingles,sheathing,and rafters and keep right on going with the new. Just make sure you do it the day before its gonna rain   probably why he doesn't want to tear of the old one.


----------



## Macybaby (Jun 16, 2006)

We have a guy down the road that did about what you are talking about. He has a house very similar to yours, and built an addition. Basically just made the house longer.

Then he put boards over the old roof and installed a metal roof that extended over the hip and over the addition. The only thing he did different is he left the hip on the far end of the house. So now it has one hip end and one regular end - I would not recomend doing that! (it looks pretty silly)

He didn't strip anything off the old roof either.

And people are right about rain - We did our roof in stages - over three summers. Every time we tore up a section, we'd have near record rainfalls (and this is SD). It got to be a joke - If we had a dry spell the neighbors would come ask us when we were going to be roofing again.

But that is what they make tarps for LOL!!









We also get high winds, and trying to put a tarp on a 12/12 pitch roof with the wind gusting to 30mph is not fun. 

Cathy


----------



## Runestone (Jan 7, 2007)

Oh Cathy, I know what you mean! We installed 3ft x 21 ft metal roofing on a 12 x 12 pitch outbuilding. This was right at the beginning of the construction. This was built entirely by DH with a little help from me (like putting the roof sheets on....in December in frigid weather)


----------



## Macybaby (Jun 16, 2006)

Runestone,

There is a company here in SD that is really pushing metal roofs over exsiting roofs. I don't recall the name right now. I'm sure they just go right over the old roof. Metal roofs are getting more and more popular in this area. We have a lot of sunshine in SD, and that really eats up the shingles. 

I think your biggest concern is going to be making sure your current roof can support the added weight. Do you have trusses or rafters? If you have trusses, they should have a load stamp on them and you can use that to help figure it all out.

My Dh and I have done almost all of our building projects. We've been told we could hire out, but neither of us likes it enough to give up our day jobs to persue it. My husband works heavy construction, and is off for the winter (his choice) and working on taping sheetrock right now. I'm excited - we may have a bedroom by the end of the month! We moved everything out of the 2 story part of the house to gut it all at once. Needed to get the weight off, as we had to jack the house up to rebuild the sill. That was not a project for the weak of heart!

Speaking of doing projects in the winter, this is one of my favorite pictures. This was December 05, and it had warmed up over freezing, so we decided to go for it. We did get it all buttoned back up before we went to bed that night.










Good luck with your roof/addition project, and make sure to share pictures!

Cathy


----------

