Spray foam insul - TX - 2" ??

[Marctrees]

Hot humid TX...

In new pole barn shop...

Will be AC'd most of our 8 month hot as Hell summer.

35 x 40 x 10 4/12 roof..

Asked for a few bids thinking 2" closed cell spray foam,,,,

THEN we would supplement w Fiberglass wide white plastic faced batts in wall and roof.

They have a name for this nowadays .. - "Flash and Batt"

First two contractors (NOT new guys, in biz for some years and reputed) say just do 2" and it will be done...

No supplement FG necessary.

Well, to me it does not make sense that that is enough R...

But they say it will be fine.

They clearly know it will be AC'd.

I thought odd they did not try to sell more inches,...

And I did get add alternate prices to make roof 3"

They both say...Sure, that is not unreasonable...

You can do that...

But any more you do not need.

They both say ROI is not there for more foam. or anything else added.

And, to make it clear, They both ALSO do blown, batts, etc.

So, who is in the hot humid south and getting by w just 2 - 3" closed cell AC'ing their shop ?

Mr.Surly... You there ?

Marc

 

[MrSurly]

Marc, I went with more than that R-value-wise and I'd like to do more(!) I used open cell 5-1/2 roof, 3-1/2 upper walls which is around R20/R13. The closed cell is about 6.7/ inch so about R14 at 2". I have no idea why they'd discourage buying more. Open cell is cheaper per 'R' and per inch. If I could have, I would have liked to put twice as much, just on principle. 2" closed cell is good, as far as I know 3 is better, 5 is better yet.
If you plan to condition the building continuously then 2" is not enough.
If I ever drywall mine I plan to simply fill the void with cellulose because, overkill.


Sent from my iPad using Tapatalk

 

[Marctrees]

Anyone AC'ing a shop w just a few inches of foam in Hot / Humid area ?

Marc

 

[mike93lx]

closed cell has about 2x the r value of fiberglass and there is a point of diminishing returns. why not have it sprayed and see how it does?

do you have a ceiling or is it open?

 

[Marctrees]

No ceiling planned.

Any and all insul will be just under roof.

New.. wide open building.

"See how it goes " is not a bad idea BUT...

That means I will not KNOW until June of next summer..

And by then everything will be moved in 100 % ++ and be in the way for further insulating.

So I need to know way before than.

Marc

 

[skippydoo]

I'm in North West NJ and I did 3 inches in the roof and 2 inches on the walls. I said to the spray foam guy, is that all I need and he said yes. I asked him if this was his garage would he do it thicker and he said no. My final question was, will you do it thicker if I want and he said you wasting your money. Closed cell is what I used, 30x40x13 wall , 5 pitch roof $7800 to spray it. The one thing I would do if your in a hot climate with a lot of sunlight is add www.atticfoil.com I am impressed with this product, it really reflects the heat back out of the roof. My roof (house) is black and my attic would hit 120 and since I added the atticfoil , its never gone over 102. Most of the time its about 10 degrees hotter than the air temp. I put a test piece in between my truss and with the metal temp of 140 , the bottom side of the foil was 30-40 degrees cooler.

 

[Marctrees]

skippy -

How long have you had this ?

Do you AC or heat regularly?

How is it working out when you condition the space ?

Thank you, Marc

 

[Barn5]

Our barn/shop is 24' x 48' with gable roof/open trusses and 16ga metal. I went with closed cell foam, 3" for the roof and 2.5" for the walls.

 

[bgarrett]

For whatever this info is worth, I sprayed 1" of closed cell on the underside of my metal roof, planning to add more. I found out that the Horrible Freight Infrared Laser Thermometer indicates that the 1" foam holds heat and is hotter than the bare metal roof next to it

 

[bgarrett]

I have wondered about using 2"of closed cell, then adding 3" of open

 

[meathooker]

2” of spray foam is supposed to count as a vapor barrier - that is a big part of the effectiveness.

FWIW I’m planning on 3” roof/2” walls if budget allows.

 

[Marctrees]

Our barn/shop is 24' x 48' with gable roof/open trusses and 16ga metal. I went with closed cell foam, 3" for the roof and 2.5" for the walls.

Barn -

So do you AC this?

Can you explain how it's working out ?

What part of Texas ?

Marc

 

[Barn5]

To clarify, I did put in a middle wall (also insulated w/ open-cell spray foam) to create two identical bays and yes I run A/C and Heat unit in each 24' x 24' bay.

Dripping Springs, TX

We've had a good number of 100+ degree days this summer and it was quite nice inside for sure.

 

[kj_mustang]

You can check my build thread. 2" closed cell everywhere, then R8 rolls of fiberglass on the walls, and another 6" of open cell foam on the roof because I had to meet Residential building code. I lived in half of the building and cool it with a 18,000 btu central ac unit. It didn't run much and we have temps in the 90's in the summer. If you are leaving walls and ceiling wide open, I would just spray 2-3" of closed cell and be done. The studies I read said over 4" of closed cell even in the most Northern Canadian climates was a total waste of money. You reach a point of no more effect from the insulation.

 

[egnorant]

2" with AC should be fine. With hot and humid you are fighting 2 battles. Spray foam will work as a vapor barrier to keep the shop dry while preventing heat flow. I had great improvement by preventing the sunshine from actually hitting the building with trees, some vines, white paint and some outside decorating signs on the walls. Set up the AC with a bit of positive pressure and pay attention to door seals and other holes in the walls (outlets, water pipes etc). This helps with moisture, dirt, leaves and such which became my big problem after insulating.

I only have an inch of foam board and spray for edges, joints and holes and temperature was not a problem any more. I was amazed at how much moisture could flow through a door with no weatherstripping or floor sweep though. Not to mention lizards, spiders and snakes!

I converted my East Texas car oven (a metal box with garage doors) to a nice, comfortable shop with a lot less insulation than I previously thought. Just handle the details and you should be fine!

Bruce

 

[dcg9381]

I'm in Texas.
I've seen many "shops" (IE hangers) done this way. Just find your local municipal airport where you can build private hangers and do a drive-by.

Traditional HVAC expertise and considering climate, education says that you really need R-30 in Texas. And this is likely true, based on some long term design around power use, energy efficiency, and initial cost of insulation, and 24/7/365 use. That being said, VERY few homes are built to R30. Almost none - at least not with traditional construction and 2x4 stick and brick walls.

I have a 60x40 building steel building, 14' eves (almost 2 stories). 3.5-4" of OPEN cell foam, probably in the neighborhood of R13-R15 cost me about $5700. That's cheaper than would it would have cost to do it myself. Consider what your garage doors are - mine are roll up, very poor insulation and require seals.

I'm "OK" with R13-R15 and feel that this is the right choice for a space that is running HVAC infrequently - say maybe 1-2 days a week for a few hours maximum. It'd be better to go R30 - for sure, but that additional $5000 will probably represent energy costs for a good number of years. And I use solar to offset.

HVAC plan is for 48000 BTUs of ductless split. IE 2 x 24K BTU units. I do not have them in yet - still working on electrical.

If I really wanted more insulation, I'd use bat insulation on top of the foam as I'm framing the building out.. Roof would have to be sprayed (easiest solution) if I wanted better R value up top (main source of heating/cooling losses).

I think you're right to stick with the closed cell stuff - harder to damage, more water resistant.

FYI - there is also a blown wet cellulose option that I've found. Cheaper than foam. I see it in commercial buildings. It's downfall is that if it EVER gets wet, you're screwed.

 

[jscoggin]

I'm also in TX and was going to start a new thread but this one is pretty similar to the questions I have so I'll try piggybacking. I'm building a stick/brick 36x56x12 shop, framing starts next week. The upstairs will have attic trusses and while there are no current plans to use the attic for living space, I plan on building for it just in case.

My plans all along were to use radiant barrier backed OSB for the roof decking, spray the entire building with closed cell insulation (walls/rafters) and install a full HVAC system. Now that construction is getting closer, I'm doing a bit more research.

I've read that putting closed cell on the underside of the roof decking cancels out the radiant barrier. As long as there are no negative effects, I still plan on using the radiant as it will cost me less than a $1 a sheet to do so, might as well.

The insulation guy I talked to said that I'll need zero venting if going with closed cell, no fans, turbines, vents, soffits, etc. This is the part that concerns me and also the part I need advice on asap as I need to frame one way or the other. I've never worked with closed cell so my knowledge is nil. Fully encapsulating a structure with no way for it to vent just seems strange to me.

I welcome any and all feedback, thank you.

 

[dcg9381]

> My plans all along were to use radiant barrier backed OSB for the roof decking, spray the entire building with closed cell insulation (walls/rafters) and install a full HVAC system. Now that construction is getting closer, I'm doing a bit more research.

Same as you mentioned above. A radiant barrier requires an "airspace" to function. No harm in using it, just the $1/sheet tax.


> The insulation guy I talked to said that I'll need zero venting if going with closed cell, no fans, turbines, vents, soffits, etc. This is the part that concerns me and also the part I need advice on asap as I need to frame one way or the other. I've never worked with closed cell so my knowledge is nil. Fully encapsulating a structure with no way for it to vent just seems strange to me.

This is 100% correct also. It's also correct for open-cell foam.
Think about it - in a traditional home, the attic is not "heated space" (meaning cooled space in Texas). The insulation is on the floor of the attic and the attic tends to build up heat in excess of exterior temperatures. That's why it's vented - ridge vents, soffit, or even mechanical air movers. It's more efficient to get rid of that built-up heat.

As soon as you foam the roof deck, the attic becomes semi-heated (semi-cooled in Texas). You really need to go check out the attic of a foam insulated house - it's night and day. The attic is now cooler than the outside air, there is no reason to vent it. In very well insulated homes, you'll need to provide a source of "fresh" air to HVAC and that's it.

For a shop - installing a fan or fans is still OK if you're not running HVAC. The shop (without HVAC) will still get hot (eventually) and you may need to move that heat outside. I'd simply mount vent-fans as high as possible, likely in a push-pull configuration.. Again, this assumes that you don't HVAC the whole thing.

 

[Barn5]

Speaking of fans to just move some air around, I went with these on a toggle switch. Quiet and they move some air...

Inline Duct Fan “Silent Series” 8 Inch, 473 CFM, 111W, Ultra Quiet Sound lnsulated HVAC Vent and Grow Room Exhaust Blower with Speed Controller and Autopilot, 36 dBA, 19.62 Lb

 

[dcg9381]

I think he's asking about moving some air "out". Which is valid. I mean, we've got big steel cook-boxes, even with insulation, they're gonna get hot if you're not running HVAC. So I favor a push-pull system at a high point in the wall, right against the roof line - 2 fans total.

In terms of moving air "around" there is no substitute for the Big *** Fan: