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Ok to put woolcell loose-fill insulation over old fibreglass insulation that is damp?

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  1. #1
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    Default Ok to put woolcell loose-fill insulation over old fibreglass insulation that is damp?

    Got a quote for new roof insulation. Guy that came to look said our old fibreglass insulation looked in decent condition but is damp. He suggested we just put a new layer of loose-fill woolcell over the top.

    We are in an 80ís two story house with a gabled roof. Roof is about 22 degrees and concrete tile. Apparently this is the source of the dampness as the concrete tiles absorb more moisture than other materials. So not sure if it will ever fully dry out (particularly given the weather here in Sydney!). The internal ceiling is plasterboard.

    As I understand, putting the new insulation on top of the old stuff is fairly common practice. However, Iím concerned about the fact that the existing stuff is damp. Should it be allowed to dry out first (if it ever dries?)? Could there be mould issues?

  2. #2
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    Is the person you spoke t a roof plumber? If not, get some advice from someone qualified. I think the comment you got about concrete tiles is pretty suspect. Sounds like a leak. Or maybe steam condensation. Is the roof lined with sarking?

    Is all the insulation damp - over the whole roof space or just in a few spots? How deep is the dampness?

    It’s a good idea to layer the insulation. But don’t cover the framing completely - so people can still see where to put their feet!

    But get any leaks fixed first - and make sure the insulation is dry before adding another layer.

  3. #3
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    Quote Originally Posted by joynz View Post
    Is the person you spoke t a roof plumber? If not, get some advice from someone qualified. I think the comment you got about concrete tiles is pretty suspect. Sounds like a leak. Or maybe steam condensation. Is the roof lined with sarking?

    Is all the insulation damp - over the whole roof space or just in a few spots? How deep is the dampness?

    Itís a good idea to layer the insulation. But donít cover the framing completely - so people can still see where to put their feet!

    But get any leaks fixed first - and make sure the insulation is dry before adding another layer.
    The OP has been given correct advice in that concrete tiles do saturate and drip.

    As to putting insulation over the damp decent condition fibreglass, a waste of money.

    No point in getting a roof plumber unless the lead flashing is leaking as roof plumbers are not usually trained/have any idea of tiles.

    My advice, don't bother with any more insulation and if concerned look at replacing the roof with colorbond.

    Do not waste money restoring the concrete tile roof as restoration is usually only good for a few years.

  4. #4
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    Thanks. Actually got a bit mixed up. He said the concrete tiles collect condensation on the underside (we have no sarking or anything) and because the pitch of the roof is only 22 degrees, he reckons the condensation will then drip down onto the insulation rather than run down the inside of the roof. He said it is generally a bit damp up there, no specific spots. So it doesn’t sound like a leak, just general dampness.

    Assuming the above is correct, then would you suggest putting new woolcell over the top of the damp fibreglass is ok (ie it will eventually dry out anyway)?

    I double checked and the guy is a qualified builder (but not a plumber!)

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    Quote Originally Posted by fency View Post
    Thanks. Actually got a bit mixed up. He said the concrete tiles collect condensation on the underside (we have no sarking or anything) and because the pitch of the roof is only 22 degrees, he reckons the condensation will then drip down onto the insulation rather than run down the inside of the roof. He said it is generally a bit damp up there, no specific spots. So it doesn’t sound like a leak, just general dampness.

    Assuming the above is correct, then would you suggest putting new woolcell over the top of the damp fibreglass is ok (ie it will eventually dry out anyway)?

    I double checked and the guy is a qualified builder (but not a plumber!)
    As Joynz said, getting the leaks fixed first is best but the existing tile roof will drip again in saturating rain so replacing the roof would be money well spent, and insulate under the colorbond with wool and siso when the roof is being done.

    The comment about condensation is an opinion and really does not hold much water. Pardon the pun

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    Ok thanks. We won’t get the roof done since unfortunately it’s too big an expense. I guess with all this wet weather it’s as bad as it’s every going to get and we haven’t had any mould problems or anything like that so probably ok to just put in the new insulation over the old stuff?

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    Usually condensation inside roofs (that aren’t leaking) is due to warm inside air hitting the cooler underside of a roof (it happens on metal roofs too).

    This is common in the evening as the outside air cools and the warmer air in the roof hits a cooler roof surface.

    The good news is that tiled roof spaces without sarking are more breezy than sarked metal or tiled roofs so condensation should dry out more quickly.

    But don’t add insulation on top of damp insulation!

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    Condensation sounds about right. We’ve had such an unbelievable amount of rain that I feel we would have had visible water damage on the internal ceiling if there was a leak. But I’m not expert so really have no idea.

    we got a quote for removal of the old stuff before installing the new insulation so might go that route just to be safe.

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    Quote Originally Posted by fency View Post
    Condensation sounds about right. We’ve had such an unbelievable amount of rain that I feel we would have had visible water damage on the internal ceiling if there was a leak. But I’m not expert so really have no idea.

    we got a quote for removal of the old stuff before installing the new insulation so might go that route just to be safe.
    But what happens when the new insulation gets wet?

    You are just moving the deck chairs … and wasting the value of the existing insulation (if letting it dry out might restore its effectiveness).

    If the insulation really is getting damp, then find out how deep the moisture is going before setting off on the same pathway with different batts…

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    Good point.

    The new insulation would be pump-in woolcell. From reading the data sheets it is hydrophobic. So it seems that, unlike firbreglass that absorbs the moisture and loses its insulation properties, the woolcell stuff repels it and maintains its R rating. I think based on this the insulation would be fine.

    I guess to your point though, what happens to that moisture? Would there ever be enough of it to actually cause a significant drip or pool on the ceiling under the insulation? Or would it effectively cause tiny beads all over the top layer of insulation and stay there until it could fry out? If I had to guess I would say the later, but honestly don’t know.

    What do you think?

    Generally speaking this house has stood as-is for 60-something years so I’m thinking whatever is going on with moisture in the roof can’t be that bad otherwise there would already be problems, right?

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    Woolcell isn’t pure wool - it is a mix of wool, paper and borax. How will the paper cope with the dampness?

    The moisture also might have been wind-driven rain coming through the tiles rather than condensation.

    What R value of insulation are you planning to have pumped in?

    An online search shows that fiberglass can retain its R value after being wet as long as it hasn’t lost volume (thickness).

    A bit of damp might be OK - as long as it dries out and the R value isn’t lost.

    I would check what your adviser meant by ‘damp’.

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    2 years ago, i said fk it and replaced the 70 year old terracotta tiles with colorbond. Since then we've had 2 la nina cycles and im so glad i made the switch.
    AFTER switching to colorbond, i had the old batts removed, the entire attic vacuumed and new batts installed.
    Big outlay, but have not had an issue since.

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