Insulation R Values

[d30gaijin]

What is the preferred/recommended method for cutting the blue/pink foamboard insulation? The local Lowe's guy didn't seem to have a clue.

Thanks,
Don

[d30gaijin]

Don, here's an update. This week I've been working in the Boston area, a little ways from home base. After dinner tonight I cruised the Home Depot and Lowes stores to see what you were looking at with the 6.5 R-value. Both stores had a lot of polyisocyanurate insulation, I suppose folks in this area have to pay attention to their insulation like you do. There was only a small selection of extruded polystyrene and very little expanded polystyrene.

Now, Lowes had 1" thick Dow polyiso 4x8 panel that had silver foil on one side and blue foil on the other....rated at R-6.5 (Home depot had a similar product that was silver foil on both sides). Maybe that's what you got, and if so, well done. The polyiso foam tends to be a light tan/off white color and usually has a foil face on both sides to slow degradation. The pink and blue extruded polystyrene have color throughout the foam, that's how you can tell the difference readily.

What I have found interesting as I've been in different parts of the country is how the box stores will favor one type or thickness based on local demand. I couldn't find any 1" board stocked in Atlanta, but it is a standard item in South Carolina...so I bought some there while working on a project at Clemson University. When I made my earlier comment, I'd forgotten that the market varies a lot, and I'd assumed your blue board was the extruded material.

Bruce

Bruce,

Your observation coincides with mine. At my local Lowe's they sell only the 3/4" blue in 4x8 sheets and 1" blue in 20" x 8' sheets, and the white bead stuff in just about any size any thickness. Absolutely nothing foil faced is offered. Very similar with my local Home Depot. They sell the pink in most thicknesses in 4x8 sheets as well with the white bead stuff, again nothing foil faced.

I emailed Lowe's "National" about it because they show multiple blue and white and foil faced on their web site but it is not available to me here in Idaho. They (their web site people) were very responsive and forwarded my email request to my local Lowe's, and the local Lowe's was very responsive to my email but told me they can't get what I wanted out here (Idaho) and that it's only available on the east coast but they could order in some "Palyiso foil faced 1 x 4 x 8 R5.9 retail is $21.26" PLUS SHIPPING... no thanks.

I find that odd because climates may be different from coast to coast in some regions, as well as north to south, but either coast can experience similar extremes in various regions. Go figure.

Do you have any recommendations for cutting/trimming the blue stuff. I hope to get started installing tomorrow but don't want to make a mess of it.

Thank you for all of your help and insight.

Don

[Trackstriper]

What is the preferred/recommended method for cutting the blue/pink foamboard insulation? The local Lowe's guy didn't seem to have a clue.

Thanks,
Don

Folks will suggest different ways. Of course it can be cut with any kind of saw but that will leave "plastic sawdust" around and that stuff can get stuck to everything with static electricity. And it's a pain if it gets in you eyes.

I've used a simple snap-off blade knife and a straightedge. These knives come in 9mm wide blades...too wimpy, 18mm wide...fine for what you are doing, and 25mm for real men, Crocodile Dundee would be proud. Lowes had "Task Force" branded 18mm knives in bulk display boxes for $2 American, that's probably low enough to buy a couple, it's cheaper than buying replacement blades. Otherwise they may be $7-8. That's the size blade that I used for cutting through 2" extruded foam using multiple passes and should serve you well.



Probably two passes will get through the 1" foam. Lay the foam on a fairly flat surface with some thin scrap plywood, Masonite, or what have you in the area where you will cut, you want the blade to hit wood or something softer when it cuts through the back side of the foam. You'll get the hang of it after several cuts, maybe two cuts approximately 1/2" deep and then a very light cut at the end to break through the back side of the foam, just scratching the backer board to save the tip of the blade.

Knives won't leave a bunch of loose particles around, just be very careful 'cause they will leave a mark on you if you're not. They be sharp. I still have some 2" foam to cut and that 25mm knife at Home Depot was just calling my name this afternoon...so I got one! I now feel extra manly on Father's Day.



And just to tease you, here's the polyisocyanurate board that you wanted to buy, and I would have too if I could have found it....it's at the Lowes right down the road from where I'm staying this week, but probably not within 500 miles of Atlanta. About $20 a sheet, and it is a light blue color on the face foil.

[Engineer Guy]

Trackstriper hit all the high points spot on. Great advice. Here's a few insights...

1. You can typically cut and snap rigid Insulation pretty much like Drywall when supported 'up' from the floor or workbench surface on a 2"x4" or edge. However, cutting it all the way through, as shown above, will net you slightly cleaner edges. For trimming or box cutouts, a serrated Bread Knife or Steak Knife works well.

2. We have foil-faced, ~R-8/inch PolyIso in our circa 1987 Tract House in CO.. Dow has stepped up to the plate to now offer similar R value Foam, as seen in Trackstriper's very nice pix. When the Foil is oriented to the warm side, as it should be, you get a Vapor Barrier function as well as a sort of Infrared [IR] reflection. I mentioned this effect above earlier in hyping 'Astrofoil'. This IR 'bounce' is a good thing no matter you achieve it.

This IR 'bounce' is difficult to equate to a 'hard' R value, but I won't quibble with whatever value Dow sticks on this effect. 'Hands on' folks have used Aluminum Foil or Aluminum plate on walls around Wood Stoves to reflect heat away from the wall.

A nice advantage of 'closed cell' Insulation, like Styro products, is that it holds R value when wet or when cut. This is one reason it's used on the outside of House Foundations or for form blocks to retain Concrete for House Footers.

Good price on that Cargo Trailer find!

[d30gaijin]

Folks will suggest different ways. Of course it can be cut with any kind of saw but that will leave "plastic sawdust" around and that stuff can get stuck to everything with static electricity. And it's a pain if it gets in you eyes.

I started out using a pizza cutter to cut the first 1/8" or so of depth (allows for a good straight cut/scribed line) then used a serrated stake knife to cut through. I did that for most of the insulation cutting for the big panels but it's hard on old hands and I knew it wasn't going to work for the 1 3/8" strips I will need for the frame center insulation. I went on Craigslist and found a cheap table saw locally for $60 that will let me cut the 1 3/8" strips straightly for the the center frame insulation installation.

<a href="http://www.flickr.com/photos/31434497@N00/4719114563/" title="Cargo inside4 by drbledsoe, on Flickr"><img src="http://farm5.static.flickr.com/4064/4719114563_7d7a101779_b.jpg" width="1024" height="768" alt="Cargo inside4" /></a>