Roof dipping under front AC

[vavroom]

Our roof is dipping/sinking under the front AC unit. When it rains, water accumulates there. Probably about 1" deep.

Incidentally, a moisture meter shows that we have moisture in the ceiling in that area (even when the water has been removed from the ceiling).


I'm looking at raising the roof back up. I found an article by the RV Doctor and it sounds like it might work. However, I'm not convinced it's the best way. He basically suggests to insert 3/4" plywood under the AC unit, under the roof membrane.


One of my concerns would be that the roof membrane might get damaged at the edges/corners of the plywood, where the roof membrane is no longer supported, particularly if someone steps on that part inadvertently.


It's definitely something that needs to be taken care of - but I'm not sure of the best way. I'm not really finding anything particular that went "ah ha!".

What does the Newmar mindhive suggest?

Thank you

[Dav L]

if the roof spars are actually bent there, then one could put a 2x6 on edge and lift up on it from the floor to the ceiling with a floor jack. That would raise the roof.
Of course this needs to be done prudently to not cause more damage than you are fixing. The floor needs some support and the 2x6 to distribute the lift load across several of the offending ribs. You will need to go higher than normal height for the joists to return to normal height. Has there been some heavy footed walking on the roof that might have bent them?

I would also take the A/C shroud off inside and get rid of all the wet insulation and replace once the cavity is dried. Not good to start a mold colony.

[Isaac-1]

Let us know how this turns out for you, I have a similar issue, though not as severe I need to deal with.

[GaryKD]

Hi vavroom,
My roof dips in exactly the same spot. Been that way since 05 new. For me, I would not worry about it. If you ever get to Newmar in Nappanee, have them look at it.

[bruceisla]

Note that I have not examined your specific model and I'm describing typical Newmar construction.


The most likely cause is that someone has repeatedly overtightened the lag bolts holding the A/C unit to the underlying A/C support frame (ignore the text on the picture).





The frame shown is welded between the roof crossmembers. The A/C unit is bolted thru the roof skin and the lag bolts go into the flat plates shown. If you overtighten the lag bolts you will draw the roof skin down toward the plate (there is some space between the roof skin and the support plate).


My suggestion is to remove the A/C unit, add some marine plywood shims between the roof skin and the square aluminum channel surrounding the plenum until the roof is level, replace any water damaged insulation, retape the duct/plenum, install a genuine Dometic gasket and a Newmar dogleg gasket, install Dometic corner rubber blocks, and properly bolt the A/C unit.


Proper bolting does NOT entail using any particular torque value since lag bolts are used. Tighten the lag bolts until the corner blocks just touch the roof .... walk around the A/C and gently lift each corner of the A/C .... if any corner block lifts off the roof, slightly tighten that lag bolt ONLY to the point the block remains in contact with the roof. This should result in the square gasket being slightly compressed and watertight. Note that genuine Dometic gaskets and blocks are required because they are denser than generic gaskets. Note that this procedure applies only to top-bolted Newmar installations.

[vavroom]

Thanks everyone for the responses. Apologies for the tardy response. It’s been a week :(

I really need to wait for several days without rain or cold (Not obvious in the Pacific Northwest at the moment!).

FWIW, There’s not been any heavy walking around the roof since we got the coach, but that was only last August. Don’t know what happened before then.

First step really is going to be to lift the AC from where it is, and go from there.

Cheers

Nic