Learn me: Roofing Edition

So, 6 months ago, we purchased a home from the 1960s.  2200 sq. ft. ranch.  We're in a hurricane zone, and it's very rainy and hot in Louisiana.  We will be looking at replacing the roof in the next year or two, and we want to make good long-term choices with it.

Right now, the plusses are:

• Hip roof
• Ridge vents at the top

The minuses are:

• Generic shingles absorb lots of heat
• Insulation covering soffit vents
• No whirligigs or other ventilation improving devices
• Inadequate insulation
• Poor installation of rooftop electrical line entry thing
• retains humidity
• bathroom exhausts to attic
• Attic is cold in winter (not a biggie), and super hot in summer (biggie). 

So, when we DO redo the roof...

1. Are there roofing materials that reflect off lots of heat?
2. Can you adjust the top layers to improve the attic situation, eg like this?  (NOTE I'm brainstorming here.  Please tell me where I'm being a knucklehead or impractical or dangerous)
   1. outer roofing material
   2. waterproof sealing layer
   3. plywood backing
   4. gap for airflow (soffit to ridge)
   5. inner sealing layer (keep main attic area sealed off/insulated from roof venting system)
   6. plywood with foam to seal air gaps
   7. foam insulating board
   8. normal attic space
   9. plywood decking on "floor" of attic
   10. normal insulation between decking and ceiling of living space
   11. Change heating/bathroom vents to go directly out of the house
3. Anything else?  Resources?

TLDR -> Tell me how to re-roof my house so that I can have a more comfortable home with lower electricity bills and don't have to worry about the roof for 30+ years (unless a hurricane rips it off).

A good metal roof is where I would put my money. Durable and last nearly forever.

It sounds like you are trying to add air gaps with extra layers of plywood- don’t do it. 

The first thing you want to do is determine where the boundary of the conditioned space is. The floor joists below, or the rafters above?  If it’s the floor joists below (like most houses),  then insulation on the rafters is not helping. 

- Use light color reflective shingles 

- Hip roofs are great for wind resistance (hurricanes), but not so good for ventilation. There is usually only half as much ridge length as there is soffit length. You are trying to create a flow-through ventilation system (from bottom to top). I am not usually a fan of whirlygigs or powered fans, but with a hip roof I’d consider them. 

- Unblock your soffit vents. You need them. 

- Your attic floor may compromise your R value. Most attic floor joists  are only 6” or less thick. You need 13” or more for a decent R value with loose fill fiber products. Your choice is A) build up the floor (and lose  headroom), or B) use a higher R value product than loose fill products. For example, closed cell spray foam.  You need R 30 or more.

- Seal EVERYTHING to the conditioned space envelope. Look at the top side of soffits in the baths and kitchen, ceiling light fixtures, electric wires going down walls, plumbing pipes, chimneys, vent pipes, AC duct penetrations, etc. You need to draft seal everything. 

- Yes, that bath fan needs to vent outside. So does the dryer vent, and cooktop vents. 

- Once the vents are clear, create the ventilation passage you want.  I would use radiant reflective barrier on the bottom of the rafters, creating a clear path from the lower soffit vents to the upper ridge vent. You want this channel creating a convection draft siphoning hot air conduction off the bottom of the roof up to the ridge. But I would leave open the reflective barrier to the attic in the top foot or so. You want the heat to rise and vent through the ridge vents. 

- Consider adding a couple solar powered mushroom type attic ventilator fans near the top of the attic space (because hip roof- you don’t have enough ridge vent). 

Most of the rest of the items you mentioned are not needed. 

Good luck!

Here’s a sketch:

You want to draft seal seal the orange line as tightly as possible. The pink line is not important to seal- you are just trying to create a space for ventilation and convection to happen. You want to stop the conduction from the underside of the roof, and move it out of the house via convection to the ridge vents and powered ventilators. 

(Notice that the rafter space ventilation and convection that’s happening is JUST like Robbie’s thermosiphon system). The only difference is he’s trying to capture the heat, you are trying to get rid of it. 

Okay, just bear with me for a second to confirm my folly.  I think, essentially, my idea was to seal the radiant barrier (which I'm not sure my house currently has) and insulate THAT in addition to the traditional horizontal insulation in the rafters.  Would it then just trap lots of hot air because the area isn't air conditioned?

Oh, and the decking vs insulation level bit: The house is severely compromised on storage space and I don't have a garage yet.   Would having a central walkway at joist level and raised decking on the sides with more intense (if possible) insulation under the central walkway and a thicker layer of batting on the rest work?  It would make accessibility the same (I'm already stooping a bit to get around) but allow for the majority of living space to have more insulation.

You probably don’t have a radiant barrier. Most houses do not. 

If you want to condition your attic, you insulate the rafters. I don’t think you want that, and you run the risk of condensation, etc. 

Notice in my sketch that the attic space still vents out through the ridge and power vent. Yours does not.  You are trapping hot air in the attic. 

The biggest problem you currently have is you have poor insulation and no ventilation. Fix those problems, and you’ll be good. 

Yes, you can have a walkway in the center. ANYWHERE it’s less than R-30 is a compromise. 

Don’t forget- heat moves from warm areas to cool. It’s trying to get into your living space. More insulation at floor level is better. 

The way I drew the radiant barrier creates a draft between 2 warm spaces, and reflects the heat that has made it through the roof back into the free-flow ventilated space. 

The way you drew it has no ventilation out of the attic. The heat had no choice but to migrate into your house. 

One thing that would be possible to try is a layer of styrofoam insulation under the plywood floor, but this is a little risky. 

The positive is that it adds good R value for the space you are sacrificing, and is very easy to draft seal very tightly.  The problem is it’s on the wrong side of the insulation, and could lead to condensation dripping into the insulation. I would definitely not do it unless you have a vapor barrier paint on the ceiling below, and even then it is risky. 

I would stick to the basics. 

Styrofoam will allow the most R value in the smallest(thinnest) material. If you want to maximize the insulation that's in the attic floor, without needing something 15 inches deep, then pack it full of foam. Spray foam is the best, because it will air seal and insulate at once, but it's costly. You can probably DIY it with rigid foam panels (preferably polyiso), and then seal up the seams with cans of spray foam for less money.

If budget is more of a priority than maximizing space, then cellulose will give you the best bang for your buck as far as R values go. But will require more depth to get equivalent R values.

I would not insulate both the attic floor and the underside of the roof deck. Plenty of new, energy efficient homes will apply spray foam directly to the underside of the roof deck, with no venting at all, and then condition the space as part of the heating/cooling envelope. But I don't think I'd suggest that here as your HVAC system probably isn't sized properly to handle the extra volume of space that conditioning the attic would entail. The simplest way is to just air seal anything/everything that you can, get as much R value as you can afford in the attic floor, make sure it's well vented (use baffles if necessary to direct air from the soffits to the ridges and keep them from being blocked by insulation), and reflect heat away with lighter shingles or special roof coatings.

Okay, definitely thanks for the insulation and convection thoughts. 

I saw someone mention metal roofs, so I have to ask about actual outer roofing materials...

shingles vs metal vs tile (tesla?) 

In reply to scardeal :

That sounds like a money question. 

Shingles vs 3X shingles vs 10X shingles (minus whatever tax incentives). 

I grew up in the New Orleans area and lived there for 44 years.   One thing to remember is that a "20 year" seal tab roof lasts 10 years in South Louisiana.  The  heat, rain, hail and hurricanes just wears them out quickly.   

Tile roofs and real slate shingle roofs look good but hurricanes in South Louisiana will blow them away.  Hurricane Betsy in the '60 blew the slate shingles off my grandparents house and some of them sliced through grandpa's metal building next door that was made of 10 gauge corrugated panels.  That's like an 1/8" of steel.

If you can go with the new metal roofing material that's what I would do. Its not very heavy and pretty easy to install.   It should last a really long time.  The old time plantations on the river used to use thin copper sheathing over tar paper; that copper sheathing lasts forever but its expensive.

Plus all the circulation, insulation and radiant barrier suggestions are valid.  

The ridge vents is what all the roofers want to do now.  Everyone used to have attic fans but the roofers started refusing to do them when ridge vents came out because the fans take a little extra time to seal them properly.  

In reply to jharry3 :

I can confirm that shingles barely last 10-years down here. Unfortunately the quotes I got for metal roofing were 1.5-2x as much as shingles, so that’s what we’re going with. They’re supposed to be a “lifetime” shingle & the roofer was up-front about them lasting closer to 20-years down here. 

The Tesla option is an interesting one in this situation...

It may completely reverse the design considerations. Solar gain is a very bad thing for most roof designs, but a very good thing for the Tesla roof. I wonder if it’s absorption reduces the heat gain in the attic, and therefore the electric load. 

And you’d have to put your electric bills into the equation. 

I’d also be curious about the warranty. Tesla shingles are warranted for life- I wonder if that includes wind damage?

Even at 10X the cost of shingles, there could be some very valid reasons to consider the Tesla roof. 

Ran across this video.  Although it's about hail, it should be somewhat relevant to hurricane damage.

https://www.youtube.com/watch?v=WMEbIxj4kRs

And I think I'm going to watch a lot of his videos....

Well, that's fun, but not that relevant.

Hail never hits a roof at 90* to the surface.  And the issue with hurricanes is not impact at all, it's wind lift. (How easily the wind coming up from the bottom of the eaves lifts the shingles)

Since you're looking at alternative roofing materials, have you looked at the DaVinci synthetic (plastic) slate tiles?  I had them installed on my house as I was done with asphalt shingle repair/replacement on my Dutch colonial.    

In reply to SVreX :

I agree that it wasn't scientific.  His other videos are quite interesting and more on-point.

some good and some bad information in this thread.

First off you need to look st the building code for your location. You may find the messing with the things you are looking at may put you in violation of the code in your area. Or force you to do things that you may not want to.

My company designs this stuff all the time. I would be glad to chat with you more via phone if you want. PM me and I can send you my direct work #.

wawazat said:

Since you're looking at alternative roofing materials, have you looked at the DaVinci synthetic (plastic) slate tiles?  I had them installed on my house as I was done with asphalt shingle repair/replacement on my Dutch colonial.    

Tell me more about this please?

We're looking at a roof replacement in 2020. A steel over roof is currently the front runner, as it seems easiest, longer lasting, and like it could handle some issues with the house. But plastics could be an interesting alternative. 

In reply to SVreX :

"Tesla insists that their solar roofing tiles will sell for a price of $21.85 per square foot. The cost of regular roofing materials is between $1-$2 per square foot for asphalt shingles."

For 10 to 20 times the price, their should be. 

In reply to lnlogauge :

Its a bad comparison.

First off, asphalt shingles don't go for $1 per SF.  $2 is fair.  

The Tesla roof is a roof AND a solar panel.  Solar panels go for more like $20 per SF (although they are not sold by the SF).  That would make the Tesla roof a little less than the cost of solar panels plus the roofing.

But you also wouldn't use Tesla solar roofing tiles for an entire roof.  You would only use the quantity for the energy generation necessary, and fill the rest with matching non-solar tiles (which cost a lot less).

So the reality is that if the Tesla solar tiles cost $21.85 per SF, the finished installed cost could be LESS than typical solar panels, and include a FREE roof.  AND have a lifetime warranty.  AND look much better than asphalt.  AND get back tax incentives.

I put in a call to Tesla to talk about my house.