Roof Condensation

[Squeeto]

Advice greatly appreciated.

The front of my motor home is molded fiberglass.

I am currently replacing the interior ceiling plywood and i see that the fiberglass batt insulation gets damp at the top due to condensation but only at the molded fiberglass area.

When I replace the ceiling plywood will this dampness go away? So don't worry.

Should I consider sealing the interior surface of the fiberglass with spray foam or TPO roofing or inserting some breathable separation or sacrificial lauan?
Would rigid foam insulation be better or make it worse because of reduced ventilation?

Crack a vent?

Thank you.

 

[rvlifer]

How damp is damp? The dampness got in there somehow so unless you figure out what caused it i wouldnt count on it going away. 1st step for me would be to ensure the roof, front seals, and windows are in good shape. If it is coming from interior moisture unless you recently had extremely high moisture inside the rv for some reason dampness inside the walls isnt a good thing.

If you have it open it is an ideal time to monitor and get more info about what is happening.

Make sure it isnt coming from outside then you can see if it dries out or stays moist and tell if something inside is amiss

 

[Kirk]

You have a condensation problem which could be excessive humidity or a lack of sufficient insulation. If warm, humid air comes into contact with the cold fiberglass, condensation is a normal result.

 

[Squeeto]

Thank you for the replies.

We are using the motor home thus condensation (no cooking, no showers).
I will search again for any leaks but it just seems that the molded fiberglass just likes to collect surface moisture.

We live in the Canadian West Coast so it can get pretty wet here. I have a dehumidifier running that extracts about 1.5 litres/day! Humidity is about 55% inside.

I have been working on the windshield wipers so the front panels are removed.
I am hoping that when the panels are replaced, it may keep drier dead air in the space.

Roxul (mineral wool) may be a better choice in this location as well.

It is not dripping wet; I am just getting ahead of a possible issue or I over-scrutinize.

​

 

[rvlifer]

Good time to beef up the insulation

 

[Squeeto]

Good time to beef up the insulation

Replaced with R12 fiberglass batt.
I considered Roxul but it is quite heavy. Seriously, I have 28 feet and only a 4 cylinder 3.9L engine

 

[Onyrlef]

Advice greatly appreciated.

The front of my motor home is molded fiberglass.

I am currently replacing the interior ceiling plywood and i see that the fiberglass batt insulation gets damp at the top due to condensation but only at the molded fiberglass area.

When I replace the ceiling plywood will this dampness go away? So don't worry.

Should I consider sealing the interior surface of the fiberglass with spray foam or TPO roofing or inserting some breathable separation or sacrificial lauan?
Would rigid foam insulation be better or make it worse because of reduced ventilation?

Crack a vent?

Thank you.

We were in Louisiana over Christmas and the humidity was so high that we were having to wipe the ceings down. It was on the cool side so we were closed up tight most of the time. My guess is that when you close it off, the warmer air from the interior won't be interacting with the cooler surface of the roof and drawing the moisture from the air.

 

[Gary RV_Wizard]

but it just seems that the molded fiberglass just likes to collect surface moisture.

That's what condensation is - humidity in the air condensing on a cold surface. The fiberglass skin gets cold because the outer layer is exposed to outside temperatures. You need to insulate the inner surface well enough so that interior moist air isn't continually depositing humidity on that cold surface. That will also reduce interior heat loss substantially, making the inside more comfortable and reducing heating costs. Before you put the plywood in, fill that area with insulation. Use the fiberglass roll (batt) type if its an irregular shape, so it can be fit into nooks and crannys. Sheet type insulation is good if the surfaces are flat and open.

 

[Squeeto]

Great advice.
Hopefully I will have a barn for the beast soon too.

 

[Adventurous Traveler]

Seriously, Gary should have his own forum for the wealth of knowledge he has, and he is so gracious to share with The Forum community. When he answers a question, you can bank on his answer.

 

[Squeeto]

Seriously, Gary should have his own forum for the wealth of knowledge he has, and he is so gracious to share with The Forum community. When he answers a question, you can bank on his answer.