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Secrets to Easy Roof Improvements with Ludicrous Benefits to You

Installation of these radiant barriers was fastener-free, and takes only minutes. Why wouldn't you install these? The return on investment (ROI) is huge.

Wanna do something pretty easy that’ll allow you to double your shop time?

Seal up your workshop and blanket it with the right layers, you’ll pretty much be able to go out there without fear of being uncomfortable.

What you want to do first is define the boundaries of your shop’s envelope.  In other words, what is the inside of your shop?  Ceiling, Walls, Doors, Windows, Floor.  This boundary is your protection from heat, cold, sound, bugs, and moisture.

In the last blog article “What To Do With Those Bare Walls”, I walked you through how I’m modifying my walls to achieve the above.  Today, we’ll walk through the roof strategy.  What’s so cool about dealing with your roof is that it has the highest payback to you, in both the summer and winter.

Note: The reason this article is kinda long is that I want it to be a reference for you later.  So print this out and have it handy as you finalize your design.

My Overall Roof Strategy

My roof strategy has to accomplish several things:

  • Temperature & Solar Control

o        Keep the summer heat out

o        Keep the winter heat in

  • Moisture Control

o        Prevent condensation on cold surfaces

o        Allow any moisture that does occur the best chance of drying out

o        Of course, general rain protection

  • Sound Attenuation

o        Keep sound from escaping the shop to the neighbors

o        Absorb sound to keep echoes to a minimum for your sanity

  • Control Airflow

o        Seal up your envelope boundary

o        Promote airflow where it’s beneficial outside of your envelope

This Black & Decker remote temperature sensor is fairly inexpensive. It’ll show you the surface temperature difference of your walls or roof sheathing with and without a radiant barrier or insulation. I was pretty surprised at how much difference just adding foil makes.

I’m dealing with an existing tile roof and roof sheathing.  But, below that there are just trusses and nothing else.  This leaves me free to do whatever I want to make it right.

From the last post, you know how awesome radiant barriers are if you live in a hot climate.  Keep in mind that your attic can get to 160 deg. F on a sunny day unless you design your overall roof/ ceiling system properly.  You also know how critical air sealing is.  I’ll be doing both here.

Air sealing is critical because by controlling all the “leaks” in your shop you can stop insects, dramatically slow heat loss in the winter, prevent hot air infiltration and loss of cool air during the summer, and prevent sound from escaping.

I started thinking about my design using exactly the above criteria, and came up with a solution to each one of them.  Then I did some research on Building, and also Energy Vanguard as recommended by Vic Hubbard at Tumblewood, (, to make sure I wasn’t forgetting anything or wind up with a moldy disaster.

Below you’ll learn how I solved each of the above requirements.

Important Note: Keep in mind what your conditions are.  What’s your weather like?  Dry most of the time?  Humid?  Or a mix of both?  If you have enough humidity, then you need to be careful of moisture migration, vapor barriers, and condensation to avoid mold issues.  Do some research; there are plenty of forums.  But be careful—everyone has an opinion and they all don’t agree, so be aware that your situation may be somewhat unique.  You can Google anything you want to know, but it may not be right for you, so get some consensus from several sources.

Sealing all gaps has 3 benefits: Temperature control, Sound control, and Insect control.

Don’t Look Now But Your Attic is on Fire!!

If you have a wood framed roof (trusses or rafters), you might as well do something about the combustibility of this space.  Why not spray or brush on a fire retardant chemical to make it harder for a fire to ignite?  Your attic can be hot and dry, and many fires are started by hot brush fire embers getting sucked into attic and soffit vents.  I bought a few gallons of this stuff, which I’ll be spraying underneath the wood sheathing and truss members before tucking in the radiant barriers.

Prior to the installation of any insulation, I spray-misted fire retardant on all the studs. This helps the wood to be less combustible. When I tested a sample 2x4 piece sprayed with this, I let it dry and then tried to ignite. It basically self-extinguished. This chemical is why the wood studs in these photos appear to be discolored.

Another thing I’m doing is using the intumescent fire-caulk left over from my walls to seal up the seams between the 4’x8’ OSB sheets.  I’m hoping this will help if there are any potential leaks.  I’m using this fire sealant.

Speaking of intumescent fire caulk, I’m also using this to seal all electrical wire or piping penetrations into the attic space, including those that go through the top plate of the walls.  My goal is to slow the spread of fire to give me a chance to escape, and maybe the firefighters more time before it’s a total loss.

The yellow stripe across the roof sheathing is a seam that I sealed with fire caulk. Just a bit of extra insurance against leaks. Once I put up the radiant barrier I won’t bother looking at the seams again unless I see water...

WoodChip Tip: Keep the utilities out of your attic like lights and dust collection ducts.  Install those below the ceiling “sealed” layer.  These items cause most of the leaks in your envelope.  I plan on using a decorative “floating” dropped ceiling and integrate my lighting in that.  Consider your envelope sacred—any penetrations need to be perfectly sealed in a detailed way.  Pretend it’s for nerve gas.  Just provide a means of fresh air intake, the best way being a mechanical energy-recovery ventilator like the ERV from Panasonic.

Roof Layer Solutions

Now that you know what you want your roof to do for your shop, look into solving each of those problems.  You can make a list like this:

  • Temperature & Solar Control

o        Keep the summer heat out—

SOLUTION: Radiant Barrier at roof line, and slow heat transfer to my shop with heavy insulation at the ceiling line.

o        Keep the winter heat in—

SOLUTION: Insulation at the ceiling level, and lots of it (R-38 or greater). This will moderate temperature swings in my shop, and mimic a cave.

  • Moisture Control

o        Prevent condensation on cold surfaces—

SOLUTION: Keep them warm or allow plenty of air flow

o        Allow any moisture that does occur the best chance of drying out—

SOLUTION: Soffit Vents and Gable Vents and a clear airflow path along roof sheathing

o        Of course, general rain protection—

SOLUTION: Quality roof tiles, flashing at valleys and penetrations, and a long-lasting moisture layer above the sheathing

  • Sound Attenuation

o        Keep sound from escaping the shop to the neighbors—

SOLUTION: Seal your envelope air tight, and bring in fresh air in a controlled manner (in my case it’ll be a residential energy-recovery ventilator from Panasonic)

o        Absorb sound to keep echoes to a minimum for your sanity—

SOLUTION: Decorative, aesthetically driven ceiling treatment using fabric-covered soundboard panels

  • Control Airflow

o        Seal up your envelope boundary—

SOLUTION: Caulk everything below the ceiling line, and all utility penetrations, avoid can lights and NO air conditioners or fan coil units in the attic space

o        Promote airflow where it’s beneficial outside of your envelope—

SOLUTION: In the attic, design good airflow from the bottom of the roof eave to the top gable vents for moisture control and to convectively cool the attic

Then you gotta make some choices.  Vented attic or unvented?  Roof with a ceiling or a cathedral style roof with the ceiling following the roof line?

Once you decide those (which I’ll discuss below), you pretty much have your roof layers.  Finally, before you start buying materials, decide the “order of construction”, what makes sense to do first, second, etc.

Vented or Unvented Roof Assembly?

Bottom line for me, the more I read the more I realized a properly vented attic space is the less risky and higher performing option.

I nudge you over to a PDF I found on Building called “Building America Special Research Project:  High-R Roofs Case Study Analysis”, by John Straube and Aaron Grin from Nov. 30, 2010.  I say “nudge” because the title sounds scary but it’s not at all; just skim through it and you’ll find yourself slowing down and reading it.

On page 4 it says “Unvented attics/ cathedral ceilings are always significantly more expensive to build in a durable manner.”  This shifted my bias away from these designs, but I wanted to still read more.  There are plusses.  By having the envelope defined as your sloped roof rather than the ceiling, you can put your HVAC and ductwork in the conditioned space rather than the hot attic.  But I don’t plan on any HVAC in my attic; it’ll be a wall-mounted mini-split system.

I read further on page 9 that unvented or cathedral assemblies aren’t very friendly with complex roof shapes with a lot of valleys and changes in pitch.  The danger that scared me most is moisture damage.  You have to seal these things very air tight (with spray foam, closed-cell) to avoid condensation on hard, cold surfaces.

It seems to me that by designing a vented attic, the inevitable wetness that will occur can dry out.  Since I live in Southern California, drying won’t be a problem.  On page 5, they mention that it is not uncommon for your roof sheathing to be 5-20 deg. F lower than the ambient temperature at night, making at least some condensation inevitable.  I sure don’t want this to accumulate so I’d like to vent it out.  Pretty straightforward, I think.

If you live in a snowy climate, venting your attic can help prevent ice dams because it keeps your roof sheathing cold, so the snow doesn’t melt as readily.  Just make sure you heavily insulate your ceiling too, so you minimize heat transfer from your shop to the attic.

Now, with a vented attic system I have the sloped roof, attic air space, and an insulated ceiling.  So, if you think about it, the ceiling is really a flat roof with a tent over it to shade it from the sun and rain.  By keeping the ceiling in shadow, you keep it cool.  But, if you don’t vent this enclosed space, the radiant energy from the sun heats up the roof, then heats up the attic air, then heats up your ceiling.

So, what to do?

3 things:

1.       Install a radiant barrier to reflect that solar energy back outside,

2.       Ventilate the attic space to convectively carry the hot air outside, and

3.       Provide a crap-load of insulation to slow any remaining heat from

making it into your shop.

Above this radiant barrier is a ventilation channel that is unobstructed from the soffit vents to the top of the roof pitch. Air is drawn from the soffit vents to the gable vent via the thermal force of hot air rising. I’m currently looking at increasing the soffit vent area to promote more even airflow, and to more closely match the free area of the gable vent.

On Page 4 of the same document, it says that, in general, it has been accepted that a properly vented pitched roof (with attic) roof assembly is the highest performing, lowest cost, and longest lasting in all climate zones, except possibly the coastal or humid regions.  But, the aforementioned is ONLY true if you avoid major air leakage through your ceiling with can-lights, ductwork, etc.  They keep emphasizing making your ceiling airtight (which is a lot easier to me than totally sealing your pitched roof airtight), so I’ll make sure I do that.

Another document you should read is also from Building, called “Roof Design”, by Joseph Lstiburek, in 2004.

Among the other alternatives out there, you could do a Vented Cathedral Roof assembly.  If you want the headroom in your shop, consider this design.  But, to achieve the necessary R-value, you might have to use foam insulation or your assembly will be really thick.  Also be careful to provide at least 2” of vent space for proper airflow.

WoodChip Tip: Don’t neglect gable wall insulation within your attic.  I’m putting a radiant barrier and foam insulation similar to my walls, and I’ll even use moisture-resistant drywall it for some fire protection since I live in a dry climate.  Also, pay special attention to the “truss heel”, the area that is near the wall-roof junction, to make sure it’s fully insulated.

Here I’ve insulated the gable wall as well, with an airspace behind the radiant barrier. Note that I face the words outward so that the side facing the airspace will be a clean reflective surface. This side of the wall will get totally covered by a rigid foam insulation sheet and moisture-resistant drywall.

If you have the correct framing, or are starting from scratch, you can consider a cathedral type roof-ceiling assembly. It has to be carefully designed, though.

So, the following is the roof construction I came up with.  Yours will vary of course, since your roof construction and requirements are probably different to some degree.

This cutaway view shows my planned roof layers. After drawing on my engineering experience, and doing a lot of reading, I decided to do this. I’m debating adding a rigid foam layer to the ceiling. The motivation for this whole thing is the lost shop time due to temperature extremes within the shop several months a year.

The following are my roof layers, from Outside to Inside:
  • Roof Tiles

This is an existing layer that I don’t plan on removing.  It’s basically like concrete, clay terra cotta-colored tiles.  It holds and absorbs the sun’s radiant energy, then so generously gives it back to me.  This radiant energy needs to be reflected back outside, which I discuss below.

  • Water Membrane, ship-lapped

This is another existing layer.  I don’t feel like ripping apart the exterior of my house right now, so I’ll leave it.  If you’re starting from scratch, make sure this is installed exactly per the manufacturer instructions, and don’t let it have any tears or gaps.  This is the one thing that’s murder to fix later.

  • Roof Sheathing

This is another existing layer.  Whether you have plywood or OSB (Oriented Strand Board), I suggest you spray on a fire-retardant.  Why not?  Cheap insurance, I say.  Does it work?  I tested it on scrap, and it self-extinguished where the untreated wood kept burning.  I guess I don’t really want to find out though.

  • 2″ or Greater Airspace

I need at least a ¾” air space to support the radiant barrier’s function.  Since I want the radiant barrier to reflect the radiant heat from the roof tile layer back outside, I want it close to this layer.  However, if you put foil side of the radiant barrier smack up against another surface, it just won’t work. This airspace serves double-duty.  My roof system calls for attic ventilation, drawing air from the low side via soffit vents at my eaves, and expelling it through my high gable vent.  A ridge vent would be better here, but it’s not how my roof was built.  It’ll put a ridge vent in my Finishing Room and Lumber Storage buildings next year.

  • Radiant Barrier

I used Enerflex radiant barriers; they come in 16” or 24” widths, and each panel is 4ft.  I just flex them to create a downward bow in the panel, and pop them into the rafter bays.  I overlap them a few inches to create a continuous row all the way from within 6” of the soffit vent to within 6” of the roof apex (peak).  They have a plastic flexible grid and some metal wires sandwiched between the two shiny radiant barrier sheets.  No fasteners generally are required.  Works really well, you could have these up in a few hours.  Ludicrous benefit for little work.  I’m prolonging the process (as usual) because I want to spray the sheathing with fire-retardant and seal the sheathing seams.

  • Attic Airspace

My roof is pitched, so below my radiant barrier I’ll have some more airspace.  This is fine, it’ll all be ventilated as part of the system.

  • R-38 Batt Insulation

I’ll be using quite a bit of insulation, as much as I can fit without squishing it too much.  There are other insulation options, which I’ll be exploring, but whether you use cellulose or fiberglass batts, be sure to NOT block your attic ventilation path.  My radiant barrier “droop” creates a nice channel for airflow that the insulation won’t block.  They sell foam rectangular “channels” to do this same thing, keeping the insulation from creeping in front of your soffit vents.

  • I’m thinking about adding a layer of 1″ or 1.5″ rigid foam insulation

This will solve the pesky problem of heat transfer from the ceiling right through the insulation via the wood truss framing.  It provides a continuous layer of insulation, increasing the overall R-value.  Keep in mind that you don’t want to expose a combustible surface to your shop if you don’t have to, so protect this foam layer with drywall.  Drywall is a good layer to use to protect combustible layers such as the fibrous sound board or foam insulation.

  • 5/8″ Drywall with beads of construction adhesive separating the drywall from the studs

For sound transmission prevention, I want to acoustically isolate the drywall from the stud framing. This is so sound vibrations will have a more difficult time passing from the drywall to the framing and on out to my neighbors.  So by absorbing the vibrations with beads of caulking, I effectively create a cushion.  I’ll put “squiggles” of caulk in the middle of each stud and let it dry.  Then I’ll carefully screw the drywall to the studs.  Yes, the vibrations can transmit via the screws, but it’s vastly better with the caulk beads than with full contact with the studs.  Thermal conduction is also slowed as well.  You’ll notice that with my crazy decorative ceiling design, I’ll have to “vault” this layer a bit, which will be tricky.  Some truss members will penetrate this layer, but that’s ok, I’ll caulk and seal these completely.

  • Decorative, sculptural layer, w/ sound-absorbent properties where possible

For aesthetic purposes, I’ll add a non-structural, non-functional layer here.  I want a sweeping, three-dimensional shape.  You could also add fire-retardant cloth-covered sound board panels for sound absorption, do a paint-fade effect, or hang ceiling sculptures.  Your lights can be designed to integrate the overall look.


This section view shows the same roof design but looking at it parallel to the truss bays. You may have noticed that my base ceiling, or envelope layer has some truss members that will pass through it. No worries, I’ll seal around those. I just wanted to take advantage of the height available between the truss bottom chords so the ceiling appears higher.


A pack of 10 of these roof-rafter radiant barriers is about 50 bucks at Lowes. It comes with 10 48”x24” sheets. Actually, these are a bit wider than 24” so that they flex to fit within the bay.

WoodChip Tip: If you live in a brush-fire area, use tightly woven attic vent screens.  The goal is to keep glowing embers from igniting your dry attic framing.  I would say use about 1/8”; ¼” is too large and allows embers to enter, and 1/16” may get clogged up with debris or paint.

Why I Need a Radiant Barrier (Posted here again for your entertainment)

The main reason I’m so motivated to get my shop temperature under control is the searing blasting heat during the summer. During July, August, and September, it’s really impossible to do woodworking after lunch. I start sweating right away as soon as I enter. That’s no fun. And it’s a colossal waste of valuable shop time. This is why your shop envelope is an investment with a super-high return.

What happens in my case is the sun blasts on the stucco layer all morning and early afternoon. This layer is about an inch of concrete. Concrete absorbs this heat, but it takes several hours for this heat to make it through to the inside. This is known as Time Lag. For example, metal has an extremely short time lag, and concrete has a much longer delay.

During the early afternoon and evening, this absorbed energy in the concrete layer is re-radiated toward the workshop, making it feel like an oven from all sides. What I want to do is reflect this radiant heat right back outside. This is exactly what a radiant barrier does.

I used my compressed air nozzle to clean the dust off of the rafters, and ran the dust collector the whole time to clean the air. Works really well; you don’t want dust on your radiant barriers so make sure that all dust has settled before you install and seal them in.

Generally a radiant barrier is a foil-like surface. It needs about a ¾” airspace in order to work. The radiant barrier can face either direction and it still works. For example, you can face the foil downwards on the underside of your roof and it’s going to do the same thing for you, which is keep the radiant heat from coming in. You just need that airspace; don’t cram it up against another surface.

I want my radiant barrier to be right near the stucco layer, so the rest of the wall doesn’t get heated up by the re-radiated energy. So, I’m putting the foil side of the rigid foam adjacent to the tar paper/ stucco layer, separated by a ¾” airspace. I’m sealing this so that I get no air movement in order to enhance the thermal barrier of the airspace, and to help with sound-proofing.

Incidentally, for my roof, I found a product called Enerflex Radiant Barrier that I’ll be installing between the truss-bays. I’ll fire spray the sheathing first, then seal all the sheathing seams with fire-caulk before installing the radiant barrier. Don’t forget to leave a channel for airflow from your soffit or eave vents to your gable or ridge vents!

Here’s a Video on Radiant Barriers from Enerflex that you will find useful.


Don’t Neglect This (Posted here again for even more entertainment!)

Once you’ve devised your best roof layering strategy, check with a contractor to see if what you’re about to construct is up to code, and just as important, won’t cause you moisture problems down the road. There is plenty of debate on what to do about vapor barriers (which you Google around for and find tons of forum comments), but you must make sure that your climate conditions are compatible with how you are layering your walls. If you totally seal a wall with a plastic vapor barrier layer, and your climate conditions combined with your indoor conditions cause condensation to form on the plastic, you could create a breeding ground for mold, especially if the area the condensation forms can’t dry out easily because it’s sealed.  How’s that for a run-on sentence?

Before You Do Anything

Prior to starting your roof project, there is some prep work that you need to do.  The first thing I did was take a shop vacuum brush attachment and clean out all the cobwebs and dust.  Then, you can use a compressed air nozzle to further clean it.  This wasn’t fun, especially since I used a ladder for most of it.

When it was super dry and hot out, I blasted the soffit vents that were really dirty with a garden hose.  It dried out in less than a day, but I let it sit for a week just in case.  But now I know it’s clean.  That’s important so that the caulking sticks properly (I plan on installing tightly woven vent screen with staples, then caulking the perimeter to keep bugs out).

This is how I applied the fire retardant. All studs are getting this treatment. When I do the roof rafter bay radiant barrier, I’ll be spraying the underside of the roof sheathing and the truss bays. Eventually my whole house will be treated as well.

The other thing you’ll want to do is seal every exterior penetration through the wall top plates by electrical outlets, lights, and conduit.  Smear caulking until it’s totally sealed.  Since I’m concerned about fire spread, I used intumescent fire caulk to seal.  Also, look for any exterior watershed or housewrap layer rips and tears; fix those while you have access.

P.S. If you’re working on your shop’s exterior envelope, read these two posts:

Some Additional Photos of my Roof-Related Fun Times:

Where the truss bays are less than 24” or 16” on center, I was able to cut these fairly easily. There is a steel wire about every 18” that goes side-to-side, so having wire cutters handy is a good idea. Otherwise I just used tin snips.

Random spider monkey.

I usually clean the radiant barrier surface before installing. This is important especially for wall sheets, since I’m sealing these in forever. Hmmm…maybe put a time capsule in one of the sealed bays? Maybe I’ll pick up a spare copy of Fine Woodworking and give someone a pleasant surprise in 2099...

For more guidance in assembling your Woodshop Design, click on the Starting? Go Here! category and read those first.

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3 Responses to “Secrets to Easy Roof Improvements with Ludicrous Benefits to You”

  1. Vic Hubbard says:

    You’re doing a great job, Bobby. I’m happy to have a woodworking site to direct questions I get in the forum. Let’s me be off work. ;o)

  2. Bobby says:

    Hey, thanks Vic. I’m glad you’re as into building design as I am!

    To a certain degree, I’m “stuck” with the builder’s decisions when they’re cookie-cutter designing these houses. For example, I’d much rather have an exterior solar control layer with an airspace to “shade” the walls and reflect the radiant energy away. When I use my remote thermometer on the same wall in the sun vs. the part that’s in shadow it was 115 deg. F vs. 88 deg. F.

    I’m considering decorative panels (and some trellises)with hidden radiant barriers in the back and an airspace to cover the sunniest parts of the walls in my backyard and the shop. The goal is to put most of the house in the shade. Solar sails are on the menu for the patio.

    I totally agree w/ you about moderating your expenses in utilities. My goal is to do high-ROI tasks every day until those things are done. To me that means getting my shop and house envelope under control, mostly for the hot months.

    You’re right about the cold months and the radiant barrier’s limited effectiveness there. That’s why I’m relying on the heavy insulation and air-sealing of the inside envelope for winter (although it only gets to maybe 27 deg. F here). Since there’ll be a lot of insulation at the ceiling, any radiant heat that is reflected back by the radiant barrier won’t have much benefit in winter. But, it sure has a dramatic effect in the summer, that I’ve seen!

    The Perfect Wall article is a great resource; I’ll be using that for my Finishing and Lumber Storage shed buildings (I like the part about the slab control layers, too). Here in Southern California, and since I live further southeast, the blasting hot July through September months make it critical to go a little crazy with the wall and roof design just to get things comfortable.

    Always appreciate your input!!

  3. Vic Hubbard says:

    Good article, Bobby. I do have to say that a radiant barrier doesn’t have nearly the effect in a heating zone. Also, when it come to moisture mitigation, it will vary, depending on the climate zone and how your particular house was constructed. If you’re doing new construction, I advise reading Joe’s article The Perfect Wall This is how houses should be built. I’m hoping I can do a deep energy retrofit on my place prior to retiring, so rises in energy rates don’t have a significant effect on my retirement income. Basically, I’ll pull the siding and roofing and completely wrap the house in several layers of rigid foam.

    Always a good read, Bobby!!


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