Roof sag behind ac

[Shane826]

I’ve had that thought and mentioned it to the factory… Instead of cutti bc a straight piece and flexing it to the shape of the crowned roof, actually cut arches out of wood.

Question… How would you insert the arches before or behind the A/C cutout?

[rickst29]

Aluminum channel might be a bit lighter, but your need for bending will require that you introduce some "V" - like cuts into he stabilizing sides. Those will weaken the stability, and they might also develop into longer and unwanted cracks under the weight of the A/C unit (e.g., when hitting pot holes in the roadway).

With wood, you could build the curved shape more accurately. I would use a single piece of high quality wood, and I would paint ALL OF IT with Laticrete "HYDROBAN" after cutting the support into shape. (If you need to use two separate pieces for street versus curb sides of the roof "shell" paint Hydroban over the joint area as well - after they are joined together.)

Unlike most other "tile substrate waterproofing products", Hydroban maintains good flexibility and DOESN'T CRACK when the substrate moves. It can easily handle 1/16th to 1/8th inch of sudden movement stress within a tiny in a joint, and the overall flex of a support can be much longer than that. It stay slightly flexible for many years.( I live in Earthquake country, BTW).

Other paint-on watroof products, such such as 'redguard' (SP?) don't stay flexible. You will not find Hydroban at any big-box hardware store, you will need to go to a large tile/stone supply place which caters to pros in order to order a small quantity. I'll guess the minimum size sold is 1 gallon, even though you need only about a quart. Expect to pay well over $100 for that gallon.

https://www.laticrete.com/en/products/hydro-ban

[Wavery]

Originally Posted by Shane826

I’ve had that thought and mentioned it to the factory… Instead of cutti bc a straight piece and flexing it to the shape of the crowned roof, actually cut arches out of wood.

Question… How old you insert the arches before or behind the A/C cutout?

You would have to cut a 1 1/2" slot(s) across the inside of the ceiling. Remove the aluminum and foam. Then epoxy the plywood arch(s) in place (in the slots) by supporting the underside of the inverted roof to form the original arch and have the inserted arch(s) adhere to the aluminum and the foam. Also epoxy the cut-out aluminum to the bottom of the arch (inside the ceiling) to achieve the original thickness. It might be a good idea to make several of those arches so that you could put them under the inverted roof for shaped support.

In order to accomplish this, I would use micro-balloon filler to thicken the epoxy resin so that it would fill all of the voids between the arch and the roof and the foam.

Let it set for 24-hours, then cover the 1 1/2" cut-out aluminum slots with 3 1/2" aluminum strips, epoxy in place. Pop-rivet the strips on both sides of the slot(s) into the original ceiling.

If one were to put a replacement arch just forward and just aft of the 14" hole (for the air conditioner) it may even be strong enough to remount the A/C. Personally, I wouldn't do it. I would install a mini-split A/C instead.

[Shane826]

Keep in mind the hole in the ceiling isn’t 14”x14”. It’s a lot bigger so the control unit is recessed up into the A/C riser.

That said, if you did one behind the bag seal the rear of the A/C cutout is like 6”-8” forward of that so it might be a bit redundant at that point.

[Wavery]

Originally Posted by Shane826

Keep in mind the hole in the ceiling isn’t 14”x14”. It’s a lot bigger so the control unit is recessed up into the A/C riser.

That said, if you did one behind the bag seal the rear of the A/C cutout is like 6”-8” forward of that so it might be a bit redundant at that point.

The number and placements of the arch or arches would depend solely on the particular roof. All I'm proposing is a theory for a possible solution.

One thing that should be considered is that a roof that has collapsed probably ha delamination between the foam and the sheet metal.