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chrisi 03-19-2010 01:25 PM

Condensation in (yet to be finished) finished attic during spring
Our attic is our bedroom... we just moved in and havent had time to finish it yet. there is already insulation that was put in just prior to us moving in. however i believe it to be incorrectly installed. It runs from the very bottom edge of the roof to the peak but is crammed in tightly against the roof walls and stapled in (it reads R-13). I thought it was supposed to have a gap left between the roof and the insulation itself to allow the air to move. Im also not sure if it should be going all the way to the peak. There will be a "ceiling" at the peak that is about a foot down from the peak and 4 feet across...

The problem is that for the past few days (in virginia) its been in the high 70s with low 40's over night and mid day to late afternoon im getting a huge buildup of condensation on the top foot of the insulation at the peak????

Ive tried reading up on it on the internet but nothing seems to apply to our situation. It only seems to have done this in the spring.

Id like to fix this problem myself but and not at all sure what to do....

Its soaked right now and im thinking of taking the insulation down and putting it back up leaving a gap between the wall (roof) and the insulation... and stapling it to the fronts of the studs....

please help!!!!!!!!!

I have photos but am having a hard time figuring out how to get them from my desktop to this site...
Also, i am completely competent but do not have a lot of know how as pertains to venting terminology and such, so please keep that in mind.

kwikfishron 03-19-2010 03:09 PM

199 Attachment(s)
Yes, there should a space between the insulation and the roof sheathing. You also need continues vents at the eave and continues venting at the ridge. Every bay needs to be vented. Take out any piece of the puzzle and you could have problems.

Bob Mariani 03-20-2010 04:49 AM

venting is only a small part of your problem.. The real issue is that you have warm moist air rising from the conditioned space below. The floor of the attic must be air sealed with spray foam. Seal around all lights, electrical and plumbing penetrations, wall top plates the attic access door the chimney (study how to do this). If you have venting at the soffits and the ridge then it should not be blocked. But fiber glass batts will not work well in the slope since wind washing will lower the R-Value. So be sure to use a sealed material to leave a gap along the roof sheathing for venting hot air. (no moisture)

Gary in WA 03-20-2010 04:37 PM

You really need to finish the attic bedroom BEFORE you occupy it. Just the loose glass fibers floating around while you sleep there sends chills to me! R-13 is not enough sloped ceiling insulation for most areas of the country:

Be safe, Gary

Big Bob 03-20-2010 06:04 PM

Chris, your pictures will help.

You advise that the R-13 3.5"

" It runs from the very bottom edge of the roof to the peak but is crammed in tightly against the roof walls and stapled in (it reads R-13)."

Is this stick frame or truss construction. (sissors truss) or a Mansard?

Did a builder advise and prepare " this attic space" to be converted into a bedroom? OR is this a nice big attic area you decided to convert to a BR?

Your insulation "condensation" issues might be well address in the LINK
posted above.

You may have some other issues you may need to consider.

Let us know.

hereslookingatU 03-21-2010 02:55 PM


You need to keep around a 50mm (2") gap between the insulation material and the roof covering and ideally there should be a breathable membrane on the side of the insulation facing the roof (in order to stop the insulation material becoming saturated), and where it does become damp it can dry out.

You are going to get condensation occur within the air gap and that is unavoidable - hence the need to be proactive and have proper ventilation as aready mentioned - the gap is acting in the same way as the gap in a cavity wall and is allowing the building to breathe by allowing the condensation to evaporate (sooner or later) the point is that the timber will not be saturated and wood rot will not be encouraged.

Ideally your rafters should be sufficiently deep to allow the insulation material to sit between the rafters and give you the 50mm air gap - if not, you will either have to adapt or replace the insulation material. If your going to have a go at thinning out the insulation material, I would recommend that you buy some disposable coverall's/overall's and a suitable face mask - as the fibreglass insulation can be highly irritable when it comes into contact with the skin, but evenmoreso from a health perspective if you happen to breathe in any of the microscopic fibres (which is possibly good reason not too dabble and simply replace!)

If you do need to reduce the thickness of the insulation material then you are going be messing around with the U value and you will likely need to consider an alternative insulation material which has a higher thermal resistivity which means it can be of a thinner section and provide similar U value characteristics. Depends on the U value for your part of the world, a solution in the UK would be to provide 80mm PIR insulation between the rafters and then back up with a 50mm insulation board which would go over and be fixed to the face of the rafters which would give you a U value of around 0.20W/m2K.
However, before you go fixing the facing board you will need to add a vapour barrier across the face of the rafters this is to keep the moisture in the warm room air on the warm side of the construction. It is the vapour in the room air that causes the problems with condensation as the air moves towards the external it cools and reaches saturation level before it can escape to the outside and can give rise to both surface and interstitial condensation.

Depending on the finish you require, you could go for an insulation board which has an integral plasterboard finish ready for tape, jointing and decoration.

Regards :)

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