EPDM vs TPO
Concluded that EPDM was the way to go for a specific case of a 12x16 foot Seed Eco-Home module. Because:
- They say that TPO is more energy efficient in the summer because it's white.
- But I'm going to cover the roof membrane with a walk-on surface (deck or carpet) so that doesn't apply here.
- It appears to be cheaper and easier to seam together TPO (with heat) than EPDM (which requires primer, glue and tape). They say TPO can come in various widths, but the off-the-shelf ones appear be 5 ft and 10 ft - so we'd have to have seams.
- But I can get EPDM in a size that is just right for my roof - with no seams at all. No seams is better than heat-welded seams :)
- EPDM is available in sheets of 20x25 and 20x50 and 20x100, which are just right for the roof sizes we do here.
- TPO sizes appear to not match our needs as well. I've seen it in 10x20 (too small for the 16x12 roof) and 10x100 rolls (way too much).
- TPO is expected to last 15 to 20 years, but it hasn't been around long enough to know for sure.
- EPDM is expected to last 25 to 30 years.
- I can get a sheet of 45 mil 20x25 (500 sq ft) EPDM for $200. We can pick it up at Menards without paying for shipping.
- TPO prices are all over the place, which probably reflects variance in thickness and quality. But I haven't found any that will turn out cheaper for this specific 12x16 roof. For example: a 5x100 roll of 45 mil TPO costs $240 - so that's $40 more than the equivalent in EPDM (and it would have seams). To that we must $300 in delivery fees. Menards does have TPO but it's either in inadequate sizes (too big or too small) or is the reinforced kind (whatever that means) that is more expensive.
- What I don't like about EPDM is that the membrane is cheap (same price as metal roofing), but the adhesive is expensive (also similar to what happens with metal roofing accessories). The EPDM adhesive costs $200 for 3.5 gallons - enough to cover 300 sq ft. An alternative is to build a deck on top of the EPDM membrane - that would weigh down the membrane so we'd only need adhesive on the edges (or maybe even no adhesive at all). If the flat roof is also a terrace then a floor of some kind (carpet or wood deck) is necessary anyway.
- TPO is no different from EPDM in this regard. It has to be attached to the roof somehow (and/or weighed down). So there's no advantage here.