I’ve heard that too, but honestly, I’m not convinced synthetic underlayment makes a big difference in attic temps. We swapped out felt for synthetic on my uncle’s place last fall—didn’t notice any real change in winter warmth or humidity. Maybe it’s more about ventilation than the underlayment itself?
didn’t notice any real change in winter warmth or humidity. Maybe it’s more about ventilation than the underlayment itself?
I’ve wondered the same. We had synthetic put on during a re-roof last year, and honestly, attic temps stayed about the same as before. Anyone ever see a difference after adding ridge vents or extra soffits? I’m starting to think airflow matters way more than what’s under the shingles.
Definitely seeing the same thing here. We swapped out old felt for synthetic underlayment last spring—no noticeable difference in attic temp or humidity, even through a pretty cold winter. I’m with you that airflow seems to be the bigger factor.
- Ridge vent install made a bigger impact for us than any underlayment change. Before, attic would get stuffy and musty, especially after snow. After adding ridge + more soffit vents, air moves way better and moisture issues dropped off.
- Underlayment mostly helps with leaks if shingles fail, not so much with insulation or warmth. It’s like a backup raincoat, not a sweater.
- Noticed some folks think synthetic is “cooler” but I haven’t seen it in practice. Maybe in really hot climates? We’re in the Midwest, so maybe it’s different elsewhere.
- If you’ve got good intake (soffits) and exhaust (ridge/gable), that’s where you’ll see real change in attic conditions. Poor airflow = trapped heat and moisture, regardless of what’s under the shingles.
I’m starting to think airflow matters way more than what’s under the shingles.
Couldn’t agree more. Only time I saw a big difference was when we had blocked soffits from old insulation—once those were cleared out, attic felt totally different. Underlayment swap alone didn’t do much.
One thing: if you’re in an area with ice dams, underlayment can help prevent leaks from meltwater backing up... but again, doesn’t really change the temp inside.
Curious if anyone’s seen a different result in a really hot/dry climate? Maybe there’s something we’re missing, but for most of us it seems like ventilation is king.
Underlayment mostly helps with leaks if shingles fail, not so much with insulation or warmth. It’s like a backup raincoat, not a sweater.
That’s the perfect way to put it. I’ve had folks ask if swapping to synthetic would make their attic “cooler” and honestly, I haven’t seen it do much except maybe make install days less miserable for the crew. I’m in the upper Midwest too—lots of snow, ice dams are a pain, but like you said, underlayment is just insurance for leaks.
Ventilation is where the real magic happens. Years ago, I had a house with zero ridge vent and only two tiny gable vents—attic was basically a sauna in July and a freezer in January. Once I added proper soffit vents and a ridge vent, temps evened out and the musty smell disappeared. The difference was night and day.
I do wonder if folks in Arizona or Texas see more benefit from synthetic underlayment, but up here? Airflow’s king. Shingles might look like fish scales, but it’s what’s underneath (and how air moves) that keeps things dry and comfortable.
Couldn’t agree more—ventilation makes or breaks an attic, especially up north. I’ve managed enough properties to see the difference firsthand.
That nails it. I see owners throw money at fancy underlayments, thinking it’ll fix heat or ice dam issues, but unless you sort out proper vents, you’re just throwing cash at the wrong problem. I’ve had tenants complain about musty smells or wild temp swings—ridge and soffit vents have solved more headaches than any underlayment ever has. Synthetic might be tougher, but it’s not magic.“Airflow’s king.”