Need To Reroof

Dudelive

Dude
Senior User
The shop is 20 x 14 block walls, original roof was tar and gravel. Before I moved here 10 years ago someone added a corrugated panel roof over top of 2 x 4s, there is a sag in the center and leaks sometimes. My question is can I remove the metal roof and increase slope to prevent leakage without removing the tar and gravel roof?
Lots have said always remove tar and gravel where others have said remove down to wood and build from there. The roof I am thinking of installing will be a shed type roof with a 12:3 or 4 pitch. With a short front steeper part. Advice will help.

Thanks
 

junquecol

Bruce
User
Does the block work extend above the edges of the roof? Not seeing actual building, my first choice would be to build up prerimeter with TREATED wood and buy premade trusses, which could be roofed with your choice of finishes, while leaving tar and gravel in place (let a sleeping dog lie.)
 

Gofor

Mark
Corporate Member
If tar or tar and gravel is leaking, it is best to remove it, especially if you plan on going back with more tar. When it leaks, the water gets trapped in the tar. When it heats up, it comes out as steam, and will promptly make a sponge out of any tar put over it. This will continue to let water penetrate. We had this problem with my MIL's roof. She kept paying people to come and retar the roof, and it still leaked. One time when I was visiting on leave, I stripped it off (it was all like a wet sponge), and went back with rolled roofing, (all I could afford as a SSGT) which stopped all the leaks. The spongy tar will also keep the rafters wet, so they will continue to degrade.
 

Dudelive

Dude
Senior User
Does the block work extend above the edges of the roof? Not seeing actual building, my first choice would be to build up prerimeter with TREATED wood and buy premade trusses, which could be roofed with your choice of finishes, while leaving tar and gravel in place (let a sleeping dog lie.)
No the blocks do NOT extend above roof. There is a 2 foot overhang all way around the building with a 8" slope front to rear of a distance of 14' block wall to block wall with 2 foot front and rear overhang. They used 2x6s for the roof rafters and 2x6s for the ceiling joists and it has a bow in center which caused the problems I think.
 

Dudelive

Dude
Senior User
If tar or tar and gravel is leaking, it is best to remove it, especially if you plan on going back with more tar. When it leaks, the water gets trapped in the tar. When it heats up, it comes out as steam, and will promptly make a sponge out of any tar put over it. This will continue to let water penetrate. We had this problem with my MIL's roof. She kept paying people to come and retar the roof, and it still leaked. One time when I was visiting on leave, I stripped it off (it was all like a wet sponge), and went back with rolled roofing, (all I could afford as a SSGT) which stopped all the leaks. The spongy tar will also keep the rafters wet, so they will continue to degrade.
Not planning to go with more tar but thinking of a metal roof and wondering does the original roof need to be completely removed.
My thought is come back 4 or 5 feet from front wall and build a 4-6' knee wall which will increase the slope enough that water will not
be a problem.
 
Last edited:

Jeff

Jeff
Corporate Member
Post some pictures of your building along with the measurements. Your original building has an almost flat roof that should be removed entirely and then reframe it to your 3:12 pitch with 2 x 6 or 2 x 8s for the span.
 

Gofor

Mark
Corporate Member
Not planning to go with more tar but thinking of a metal roof and wondering does the original roof need to be completely removed.
My thought is come back 4 or 5 feet from front wall and build a 4-6' knee wall which will increase the slope enough that water will not
be a problem.
Then the answer to your question is : It depends. The deciding factor would be the condition (strength) and size of your current roof joists. If you put in a knee wall, or vertical roof supports, your current joists have to bear the weight of both the old and new roof. Normally, knee walls are supported by a load bearing wall beneath them. With the old roof already sagging, that indicates the condition of your joists are already not up to the task. Removing the old roof may allow you to just beef up the weak joists, but maybe not. If you use trusses instead of the knee wall, then the weight of the new roof is borne by the walls.

From a practical standpoint, trying to install a new roof over an old is very frustrating and time consuming, as you have to cut through the old roof for all your attach points. From a volunteer firemans' standpoint, we hate double roofs whenever a fire gets into that space, as it is very hard to impossible to safely gain access to put out the fire as well as to locate any fire still remaining. So, for ease of work, weight considerations, and fire safety, I would recommend removing the old roof.

Just pointing out concerns that I would have. I am not an expert, so would go with someone here with more construction or architectural experience for the best fix to meet your needs and budget.

Terminology that I used:
Rafter: the board that holds the roof material
Joist: the horizontal boards from wall to wall. They hold the ceiling material as well as keep the walls from spreading.
Truss: a manufactured (on site or commercially) assembly of triangles that support the roof, and may also have the horizontal boards to hold the ceiling. Due to the strength of triangular construction, trusses can sometimes be made of smaller dimension lumber, depending on the truss design.

On a flat or single slant roof, the joists and rafters are often the same board.

All readers, please feel free to correct anything in the above that I have wrong.
 
Last edited:

JimD

Jim
Senior User
Would an option be to wait to remove the existing roof until the new roof is at least framed? I would not want to leave the old roof but I can see why it would be handy to not have the building open to the sky and then potentially run into a snag and not be able to close back up before it rained or something. It seems like it would complicate things to leave it even temporarily but it might also add enough peace of mind to be worthwhile.
 

Dudelive

Dude
Senior User
Then the answer to your question is : It depends. The deciding factor would be the condition (strength) and size of your current roof joists. If you put in a knee wall, or vertical roof supports, your current joists have to bear the weight of both the old and new roof. Normally, knee walls are supported by a load bearing wall beneath them. With the old roof already sagging, that indicates the condition of your joists are already not up to the task. Removing the old roof may allow you to just beef up the weak joists, but maybe not. If you use trusses instead of the knee wall, then the weight of the new roof is borne by the walls.

From a practical standpoint, trying to install a new roof over an old is very frustrating and time consuming, as you have to cut through the old roof for all your attach points. From a volunteer firemans' standpoint, we hate double roofs whenever a fire gets into that space, as it is very hard to impossible to safely gain access to put out the fire as well as to locate any fire still remaining. So, for ease of work, weight considerations, and fire safety, I would recommend removing the old roof.

Just pointing out concerns that I would have. I am not an expert, so would go with someone here with more construction or architectural experience for the best fix to meet your needs and budget.

Terminology that I used:
Rafter: the board that holds the roof material
Joist: the horizontal boards from wall to wall. They hold the ceiling material as well as keep the walls from spreading.
Truss: a manufactured (on site or commercially) assembly of triangles that support the roof, and may also have the horizontal boards to hold the ceiling. Due to the strength of triangular construction, trusses can sometimes be made of smaller dimension lumber, depending on the truss design.

On a flat or single slant roof, the joists and rafters are often the same board.

All readers, please feel free to correct anything in the above that I have wrong.
I took your advice on the roof and had it replaced completely. The people installed a "vinyl" like is used on malls and large roofs.
they did remove all the tar and gravel and replaced rafters with new ones. also the new roof now extends over the deck. Thanks for the advice of fire safety.

Dudelive
 

Sourwould

Taylor
User
Be careful if you even have to walk on that rubber roof. The white stuff punctures easily. Same if you have trees around and get a big branch falling. It's easy to patch though.

I think that's a great replacement for tar and gravel.
 

Dudelive

Dude
Senior User
Be careful if you even have to walk on that rubber roof. The white stuff punctures easily. Same if you have trees around and get a big branch falling. It's easy to patch though.

I think that's a great replacement for tar and gravel.
Complete tar and gravel was removed and new wood replaced where it was needed. There are no trees around for limbs to fall and puncture. Thanks for the warning.
 

Oka

Oka
Corporate Member
Hmmm, if it were me I would remove both roofs and then start from there. 20x14 is less than 300 sq.ft.

Given it is less than 3 square of roof I would just refame it to what my needs or wants are.

Building code Roof span chart would dictate either 2x6 @ 16" on centers or 2x8 @ 24" for clear span 20lb load 1/240 , if you go 1/120 (1 foot deflection in 120 ft.). then just 2x6 @ 24 o.c. would be ok. Either way, always do the roof right and with quality, sucks having a leak on the roof.
 

Dudelive

Dude
Senior User
Yes the roof was completely removed down to the rafters and all damaged rafters were replaced.
The people did an excellent job on the repairs now to finish the close-in and insulate. Thanks for the reply


Hmmm, if it were me I would remove both roofs and then start from there. 20x14 is less than 300 sq.ft.

Given it is less than 3 square of roof I would just refame it to what my needs or wants are.

Building code Roof span chart would dictate either 2x6 @ 16" on centers or 2x8 @ 24" for clear span 20lb load 1/240 , if you go 1/120 (1 foot deflection in 120 ft.). then just 2x6 @ 24 o.c. would be ok. Either way, always do the roof right and with quality, sucks having a leak on the roof.
 

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