Replacing rotten flat roof deck board from above

[GlennSpray68]

Hi all ,

I hope someone can help with the following issue I have discovered.

recently whilst on my flat garage roof, I noticed a particular area 600mm x 400mm approx, that was very springy/spongy . I believed the decking board underneath has perished and needs replacing.

I haven't had chance to investigate further the cause of the deterioration of the board.

Unfortunately the ceiling below is plaster boarded, dpm'd and insulated, with no means of access from below .

I am hoping I can cut out the rotten area back to the nearest joists (with a multitool) and replace with marine ply of the correct thickness and isoflex afterwards.

The roof has had in the past a liquid membrane treatment for weatherproofing.

If I establish the thickness of the decking board . is it feasible to cut out the area(using a circ saw at 45 degrees, finishing the corners with the multi tool) to allow a mitre joint at the joins and glue the board in place with titebond or similar.

Obviously I would again cut back to joists and if possible put in battens perpendicular to the joists.

Any advice or suggestions would be very gratefully received.

Many Thanks in advance

Glenn

 

[JP_]

I am no expert, but, if the joists need replacing, surely the plasterboard, dpm and insulation will all need to come off first - otherwise, what will be holding it up when you remove the joists from above?

 

[bobasd]

post photos of the whole roof area an the spongy area in detail from above an from inside the garage showin the ceiling below the damage.
dont cut anythin yet and deff dont remove any joists.

 

[GlennSpray68]

Hi guys thanks for the replies, I think I may have confused you, I believe it is the deck board not the joists that has perished I will know more when I have had a chance to look at it in more detail Fri night. Thanks for the replies much appreciated

 

[datarebal]

Hope you don't end up like this..

 

[GlennSpray68]

Hope he didn't get any insulation in his skin ! itches like a bleeder!

 

[GlennSpray68]

Hi All , I have inspected the spongy section of the roof and as I feared, the wooden board underneath has rotted. I believe this is due to the seam failing at the felt join.

The area of rotten board is approx 4 ft x 16 inches (the area within the 2nd image white line)

Third image shows direction of sagging towards rotten area.

I am aware that I will have to cut the board back to the nearest joists to get a good support.

My idea is to cut the board back to the nearest joist, replace the board with marine ply, which I will pre treat with water seal , then re-felt and finally seal with ISOFLEX liquid rubber , I will probably do the whole roof while I'm at.

Any suggestions or other ideas as how to deal with this.

Many thanks once again for all your help

Glenn

 

[bobasd]

pretty straightforwd for whats to be done next but i dont see photos of the whole roof an the garage ceiling?

 

[GlennSpray68]

Hi bobasd, I have removed the boarding which was soaking back to second set of joists leaving an area of 1200x1200 to reboard, unfortunately the joist at the blown seam is badly rotten I intend to sister it on both sides after cutting away all the rotten wood and repairing it with a new timber insert .
What do you think
Cheers Glenn

 

[GlennSpray68]

Hi forgot to ask you, would it be an idea to treat the replaced board with isoflex before felting over the top or will it affect the felt adhesive, added the photos as requested
Thanks for all your help much appreciated

 

[bobasd]

i think your goin to have to go the route datarebal pictured.your roof has been worked on before an its time for a new roof cover.
as you strip the roof you could find more deckin an joists are affected?

storin heavy stuff on the roof might not allow for expansion an contraction an allows debris to colect.are you goin to keep stuff up there?

thers no flashin at the abutment but cant tell if its a problem or not.

 

[GlennSpray68]

Hi bobasd, I'm going to remove everything from the roof, there is some flashing and it's pretty sound, apart from where I have levered it up for access. I'm going to to replace the board and joist and then treat it all with a couple of coats of liquid rubber. Hopefully this will get me through the winter and then I think I'll look at getting it all done or put a new pitched roof on next summer,
All these weeks of dry weather soon as I start on the roof it starts bleeding raining