Foam over existing duct insulation...?

You know, considering I make a living with mechanical failures, it just
seems more prudent NOT to cover the ducts with something as permanent as
expanding foam.

Vapor barrier: is needed to protect [from the warm side] moisture
penetration. Flexible ducts come with a vapor barrier, batted insulation
comes with a vapor barrier.

Thinking that, the foam is layered on top, and you're not foaming under the
ducts, you'll be leaving an area adjacent to the ceiling without protection.
You'll be adding some weight to the duct(s) increasing the crush weight for
any insulation on the bottom.

I'm not a big believer in foam as it makes it difficult to repair /change /
correct things afterwards.

Good luck...

--
Zyp

Posted by New Directions In Building Ser on March 22, 2008, 5:09 am

Interesting concept - did anyone ever think about the fire hazard rating of
using polystyrene or polyuretane product to fill spaces. This is of concern
and does need careful consideration.
In commercial premises we have thankfully outlawed the use of expanding
polyurethane foam as a sealant for penetrations between compartments.
Duct insulation is required to abide by specific flammability and smoke
generation indices -
Check out what you're doing with your local regulator and make sure that
they endorse it - otherwise you may have just voided your insurance and if a
fire impacts upon any of your neighbours due to such an installation, you'd
be fully liable for any losses that they may incur.

> Kenneth wrote:

>> On Fri, 21 Mar 2008 10:59:03 -0400, Kenneth

>>> On Fri, 21 Mar 2008 07:46:34 -0700 (PDT), "KAubert

>>>

>>>> I will say this; I have seen where loose fill was applied completely

>>>> over ducts and made very nice stain tracks on the ceiling. I can see

>>>> where condensation could be a problem with foam covered ducts;

>>>> especially if open cell foam were used.

>>>>

>>>> Keith

>>> Hi Keith,

>>>

>>> Can you say something more about why the (potential)

>>> condensation problem would be greater with open cell?

>>>

>>> Thanks,

>> Hi Again Keith,

>> I have continued to think about your comments above, and

>> realize that we have no condensation problem whatever

>> despite having fiberglass simply laid over the ducts.

>> We use lots of AC for several months of the year, but I have

>> never noticed so much as a drip.

> Normally proper sized ducts seldom condense.. Smaller ducts do and should

> be insulation wrapped to prevent such.. prior to putting in either Loose

> fill or bats.. I still recommend bats for future maintenance.

>> All the best,

> --

> Posted via a free Usenet account from http://www.teranews.com

Posted by Zyp on March 22, 2008, 3:25 pm

New Directions In Building Services (Australia) wrote:

> Interesting concept - did anyone ever think about the fire hazard

> rating of using polystyrene or polyuretane product to fill spaces.

> This is of concern and does need careful consideration.

> In commercial premises we have thankfully outlawed the use of

> expanding polyurethane foam as a sealant for penetrations between

> compartments. Duct insulation is required to abide by specific

> flammability and

> smoke generation indices -

> Check out what you're doing with your local regulator and make sure

> that they endorse it - otherwise you may have just voided your

> insurance and if a fire impacts upon any of your neighbours due to

> such an installation, you'd be fully liable for any losses that they

> may incur.

Best advice yet.

--
Zyp

Posted by on March 22, 2008, 9:09 am

wrote:

> On Fri, 21 Mar 2008 07:46:34 -0700 (PDT), "KAubert

> >I will say this; I have seen where loose fill was applied completely

> >over ducts and made very nice stain tracks on the ceiling. I can see

> >where condensation could be a problem with foam covered ducts;

> >especially if open cell foam were used.

> >Keith

> Hi Keith,

> Can you say something more about why the (potential)

> condensation problem would be greater with open cell?

> Thanks,

> --

> Kenneth

Kenneth,

I agree with the comments about not foaming over the ductwork. If you
ever have to do electrical or other work up there, you'll be cursing
yourself.
Instead, move the ducts into the conditioned living space. Foam the
underside of the roof deck with high density polyurethane. 5+ inches.
Seal the entire attic air tight, just like you would living space. No
roof vents. No soffit vents. Foam and seal.

This has the added advantage of negating the energy loss due to air
infiltration through any penetrations in the main living space
ceiling, through the walls, etc. It a real bear to properly air seal a
home by sealing every seam in the attic, so you negate the issue by
enclosing the attic along the roofline.
consult the following document for the science behind this approach:
http://www.buildingscienceconsulting.com/resources/roofs/unvented_roof_summary_article.pdf

The home is a complex system. Make sure you understand the
ramifications. Be especially careful about moisture drive from the
living space into the attic, regardless of what you do. Seal around
bathroom fans and lights; make sure that fans vent properly through
roof vents; if you have a whole home humidifier, make sure you have
hygrometers around the house to ensure your not over-humidifying and
remember, a tight house probably won't need humidification anyway.

There's more to this than insulation. Keep doing your research.

-tdi
Energy Testing & Consulting

Posted by Kenneth on March 22, 2008, 9:18 am

On Sat, 22 Mar 2008 06:09:40 -0700 (PDT), tedinoue@gmail.com
wrote:

>I agree with the comments about not foaming over the ductwork. If you

>ever have to do electrical or other work up there, you'll be cursing

>yourself.

Howdy,

Can you please say more about this aspect of your
interesting comments?

When you use the term "up there" I don't know what you mean.

We have under consideration foaming the sides and top of the
ducts that run along the floor of an attic space.

How might that become a hassle if we were to "do electrical
or other work up there" in the future? I ask because the
rest of that attic space would be untouched.

Sincere thanks,
--
Kenneth

If you email... Please remove the "SPAMLESS."

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