Roofing/Insulation Question

[Brian_Weekley]

I'm in the final stages of my timber frame barn construction and would like to revisit a previous question from way back about insulating the roof.  This building is intended primarily for a workshop (in Maine).  It will have a wood stove for heat in the winter.  I was planning rigid insulation over the decking with furring strips/strapping to attach the tin.  How thick and what kind of insulation should I use?  If it were a house, I'd use the polyiso.  But that's pretty expensive for an outbuilding.  Is it OK to use the blue or pink foam board instead?  Maybe cover the top of the foam with a radiant/foil barrier to reflect some heat to keep it from getting too hot?  Looking for recommendations...

Thanks, Brian

https://forestryforum.com/board/index.php/topic,55767.msg806766.html#msg806766

[Satamax]

Have you thought about strawbale?

Only prob is finding someone who has a small square baller. Thoses don't exist anymore in your country i bet!  ;D

[S.Hyland]

Hi Brian,
   The blue or pink stuff (extruded polystyrene) will be awfully expensive for what you are using it for.That is normally used for under slab applications because of it's higher compressive strength. Have you considered used polyiso? I've had pretty good success finding it on commercial re-roofing jobs like schools, for cheap or free. There are also a couple sites that sell it online like Insulation Depot. I would put at least R25 in the roof if it was me, which is 4" polyiso.
Good luck with it!

[Holmes]

 S.Hyland has a great idea.  I just saw 2 1/2" polyiso used for sale on CL for $12  for 4x8 sheets central Ma. area. It may be wise to check in your area.

[giant splinter]

Brian,
I use an insulating material called MBI (Metal Building Insulation) it is made just for your application, it is important to use a material that will prevent the condensation from building up under the metal (it will be dripping down your neck like in my old barn).

[Brian_Weekley]

Unfortunately, my building site is 300 miles from where I live and I'll have very limited time available to complete the roof--time and efficiency are key.  If time and transportation weren't an issue, I would definitely go the Craigslist/used route.  However, I can't count on the availability nor have the time and means to transport it.  Most likely, I'll have to bite the bullet and have it delivered by the local lumber yard directly to site.  I'm really looking for the best type, thickness, and cost effective option.  I was planning for 4 inches of polyiso unless there is a better alternative.

[Thehardway]

Brian,

There is a fine line between miserable failure and great success at what you are attempting. 

Get it wrong and when it rains outside, it will literally pour in your barn.  Get it right and you will have the dryest and most comfortable barn, all year long.

Barns and old style timberframes (non-sip enclosed) were intended to breathe.  As moisture escapes from the timbers, it needs a place to go.  If this moisture gets trapped against a roof and the temperature of the inside roof surface is below the condensation point, it will condense and run down the roof, drip onto your floor or worse yet, rot out your timbers and roof members.  You will get mold and mildew issues unless you install an air exchange ventilation system with humidity control.  If you have large animals inside in the winter this will be compounded 100X.  They will likely develop a respiratory disease

So how do you avoid this situation?  Well, the easiest is by making sure that there is always a thermal buffer and the condensation point cannot be reached on bottom of the roof surface. or if it can, that you have a drainage plane.  This is easily accomplished in sips as there is no air passage through the sip and thermal change is graduated.  Tar paper on top forms a drainage plane under the tin. What if you can't afford sips?  My advice would be a  roof system with spray urethane foam.  This may or may not be cost effective depending on the size of your barn. But I would bet it would beat wrap and strap of 4" rigid polyiso in both cost and performance and ensure a dry, comfortable barn.

Here's how. Build your roof and lay your tin in the same fashion you would on an un-insulated pole barn screwing your roof metal to 1"X3" 18" OC with one layer of felt paper under it. (felt paper serves as a backer for the foam and dissipates any moisture that may develop on back of metal from corrugations or soaking into and rotting your 1X3 and it also allows easy replacement of tin down the road.  It will get you dried in fast and simple.  After the roof is on and you are dried in, hire an insulation company to come out and spray the under side of the roof with 2" of closed cell urethane spray foam so that the underside is completely sealed and covered. 

I know that 2" does not sound like much but this 2" of closed cell urethane will prevent air movement through the roof as well as thermal migration. Because of this, 2" of foam can out perform 4" of rigid strap, 8" of EPS  or 13" of batt style fiberglass.  At the same time it prevents condensation problems.

You will find yourself cool in the summer and warm in the winter with minimal energy expenditures.

Think of it this way, an igloo cooler uses about 1" of urethane spray foam in the walls and lid.  A well made one will keep ice for 7 days in 80F ambient temps. without condensation on the outside.  Likewise, a well made barn with 2" of urethane insulation well sprayed without gaps will keep 80F inside temps when it is 32F outside, without condensation.

Once again, be careful, the devil is in the details.  Better to leave it uninsulated and burn lots of wood than insulate it wrong, burn lots of wood, be wet, and get sick.
We could discuss the "green" aspects of spray foam and embodied/expended energy but that get's tedious and boring real quick.

http://www.sprayfoams.info/foam/the-r-value-myth/

[losttheplot]

You can also get the spray foam as a DIY "kit". It comes in two cylinders, the size of BBQ propane tanks.
I just used two kits in a crawl space, its pretty easy to do, but its not cheap.

Might be an option if your in a remote area.

LTP.

[jueston]

I have priced out the DIY spray kits, and if your doing a real small job, it prices pretty close to having a pro do it, because they charge a lot just to show up and set up there equipment. but if your doing a big job, then the pros cost less. I don't have any experience with the product, so I have no idea if the quality is the same as the pros, but there are lots of different companies who make spray foam and they all have a slightly different formula, so I assume there is some quality difference there...

for the purposes of comparison, this might help the OP, in my area I can get spray foam 3 inches thick at a little less then $3 a sqft. I don't know if everyone can get a that price, I do a lot of business with this vendor, and it varies by area, and I'm sure it varies by season and the price of oil too...

[Brian_Weekley]

I prefer not to use spray foam on the interior underneath the decking.  Since I'm not planning to finish the interior, I don't want to look at the spray foam between the rafters.  Besides, after spending my time to build a timber frame, I want to see the wood on the inside!

I've attached a diagram below illustrating what I was thinking.  Felt to cover the roof decking.  Taped poly-iso insulation (2 layers x 2 inches) with foil covering.  A rain-screen type of lattice on top of the insulation would both secure the foam and be used to attach the tin.  With vents, the lattice would also provide airflow to dry any condensation or extraneous water under the tin.  Is this a reasonable layout?  Do you see any problems with this configuration?

[razor]

I'd be inclined to follow TheHardWay's advise. My timber frame shop is insulated almost identical to your drawing, only I have drywall as a ceiling. 6 mil poly over that, full dimension 2x4's on edge 24" apart with extruded styro between. 1" styro over that followed by 1x3 strapping and finally tin.
A warm morning sun after a cool night and the underside of the tin is dripping wet. So far the 6 mil poly has kept the drywall dry but it won't forever.
It's been 10 years but I know I'm going to have to pull it all off in a year or 2 and redo it all.

To keep the look your after from the inside I would spray foam from the top before you lay the tin. Doing that will still leave you a gap under the tin, not the best as HardWay says but with roofing felt over the spray foam you can at least drain condensation away.
The thing is, if there is space under the tin, it will be wet there when conditions are right

[shinnlinger]

A few years ago, someone on this site turned me onto a Massachusetts company that sells used poliiso on ebay.  I bought a whole semi load for 5 grand from a lumber kiln in Maine,  It was something like $8 a sheet for 2" 4x8 sheets in pretty decent shape.  I was cutting some up today coincidentally.

Dave

[shinnlinger]

I think it was these guys..http://www.greeninsulationgroup.com

look up foam roof and you will see a few ideas in the archives as well...

[Satamax]

Razor, if your roof is done right, it shouldn't go through the insulation.

Over here we use a drip screen on top of the insulation. But direct contact with the insulation is forbidden.. Vapor barrier on the  inside, insulation, osb usually on top of the insulation, then drip screen, then lattice and steel. I use sarking of boxed method. I like boxed.

Brian, what's your requirement for heating, energy efficiency etx. Because your proposed insulation seems awfully thin to me. With the new euro rules from 2012, i can't put less than 10 inch glass-wool in a roof, or 8 polyurethane foam. That's R8 (but we don't seem to calculate the R as you do.) in 2020 we'll be gone for passive. R10 for roofs, R6 for walls. Remember, that euro r values. R10 should be around 30cm of glass-wool. And i don't talk about wood fibers or wood wool. I've put 32cm of this in the last roof I've done. Just for a R of 8.

[Brian_Weekley]

Brian, what's your requirement for heating, energy efficiency etx. Because your proposed insulation seems awfully thin to me.

This is not intended as a house.  This is only intended as a small barn/workshop.  I'd like to heat it occasionally with a small woodstove when I'm working out there in the winter just to keep it comfortable.

[S.Hyland]

Hi Brian, 
On top of your foam layer you could run an adhesive backed ice and water shield. Some of those products are rated to be exposed to the elements for a year. Under the steel they would let condensation run off under your airspace indefinitely. I would do just like you have drawn, with the addition of the ice and water shield.
Also, you can have the used foam from insulation depot delivered anywhere. I don't know if the trucking cost would wash the savings but it might be worth checking out.

[giant splinter]

Brian,
It is a little bit difficult to see the detail in the overhang(eve-roof overhang) in post nine, I was just curious if there is an overhang (eve) are you planning to run your insulation all the way out to the facia board or outside the plate line or building line?. If your plans are to run your insulation out beyond the building line into an overhang perhaps the use of frieze blocks could be used to reduce the cost of your insulating material bill. If I somehow have mis-interperated your drawing then please disregard this post.

[shinnlinger]

Here is what I did...

[shinnlinger]

Brian,

In looking over your diagram, I believe I did almost what you proposed there.  I staggered the seams on three layers (as opposed to 2) and did not tape or foil because that would have been a PITA and more $.  I attached the vertical 2x4s to the purlins of the frame using 11" panel screws(cheap on inter web).  I predrilled the 2x on the ground where the purlins would be so I could just stick a screw in the hole and go when I was up on the roof.  Out of 500 screws I only missed 2x.  I then horizontally strapped over the 2x and screwed tin to that.

Dave

[Thehardway]

Brian,

I understand you don't want spray foam visible on the inside. In the method I describe, you can install 2X material left proud on the rafters. This gives you your 2" cavity for spray foam, then the T&G "decking" is applied to the underside after the foam is applied.  This gives you the same look but with faster dry in time and better performance.

If you really just must have that authentic T&G decking applied directly over the timberframe, here's how.  Install the decking, place a felt paper over the decking, install 2x material over decking to get your cavity sleeper style, spray the assembly with foam incuding a skim coat over the 2x material.  The foam should cure with a slick finish, sealing the wood.  This slick finish will shed any dripping condensate if there is sufficient pitch.  Put your 1X strapping on top of the foamed over 2x and screw it down tight so the foam forms a gasket seal. Now install your tin. You can place another layer of Felt paper between strapping and tin to protect strapping from moisture and rot.

Are you using a corrugated steel, if so air will circulate well under it and dry it out (Don't use sealer strips at top and bottom, let the air flow and install fascia to allow for air flow and condensate drainage.  If you put a black ridge cap on, it will create a thermal draft in the slightest sun and dry things nicely.  If you are using a 5V or standing seam then you will need to create some air channels to keep it dried out.
the
I doubt you will find taping seams on polyiso a suitable means of creating a waterproof barrier.  Condensate will find its way through and you will end up with that pretty decking messed up from water stain, warped, and likely rotting on the back side.  If nothing else, the moisture will migrate down through the foam around the strapping screws or nails.   

The wrap and strap method is much better suited to a asphalt shingle or wood shake style roofs as they are not as prone to condensate buildup for many reasons.

The radiant foil barrier is a waste of time and money. Adhesive ice and water shield is $$$.


Another method is to do similar to described above but use your polyiso blocks or EPS cut to fit between 2x and then spray the edges and over the 2x.  This will accomplish the purpose of a complete seal and vapor barrier but without the cost of complete spray foam or the pain and $ of taping seams.  You can do this with the Foam It tank kits.

I have seen way to many dripping steel roofs in cold climates.  A light wet spring snowfall followed by a warmer 35F-40F, foggy, still day  (I assume you get those occasionally in Maine) could be disastrous to your building not to mention your tools
and equipment which will all get dripped on and start to rust.

It is your building, budget and time and ultimately you decide what you think is best.  I am just sharing from past mistakes.  In Virginia we have a lot of cold, humid, still days in winter spring and fall that can amplify condensation issues.  Others opinions and comments are just as valid and likely reflect their experience and regions climate.  I have spent some time in the Adirondack region and know spring and fall, and also a few summer days in Alaska.

Good luck to you and be safe on that roof!

[frwinks]

you've prolly seen this, but jic ;D  With enough air flow under the tin, no need to worry about condensation ;)

[Brian_Weekley]

Thanks for all the information to consider.  Here's one thing I'm struggling with:  I typically think of using a thin coating of spray foam on the inside of walls/ceiling to primarily eliminate air infiltration.  However, if I were to spray the underside of the roof decking (from the inside), it seems you would still have the concern of condensation from under the tin making its way down to the decking.  Therefore, it seems the most important thing is to have a good barrier under the tin and good airflow to keep things dry.  Do any of you folks have tin on SIPs?  What's keeping the condensation from rotting the top layer of your SIP panels?  Makes me almost think tin isn't worth the trouble with all these condensation/moisture concerns?  I guess there are advantages sticking with sheathing over polyiso, felt, and conventional shingles instead?

[bmike]

I wouldn't put a metal roof directly on a SIP panel. (I actually wouldn't put any roof directly on a SIP panel).

I'd build a cold roof, even at greater expense, by adding a layer of strapping and another layer of sheathing.

[johnvansoest]

I'm a new user and have a question along the lines of the discussion in this forum.  I have an old post and beam barn structure that was converted to a special event space about 80 years ago (33' x 62').  It is finished inside with various wood and plaster surfaces that I can't disturb, nice wood floor, has heat and A/C, but has never been insulated.  It is used almost exclusively in the summer/fall, and can get hot inside when the sun is really beating down and it's filled with people (sometimes 150 guests).  I plan to do a reroof soon, probably this fall, and when I do I want to insulate from the outside using foam.

The method we are settling on is a variation of wrap and strap:  we will:

-  strip of the existing asphault down to 1/2" ply that was installed on top of 1" roofers about 25 years ago.

-  install a vapor barrier over the ply - a product called titanium, which will also be the temp roof

-  lay two layers of foam over everything, totalling 3-1/2".  Don't have the space for much more...

-  lay 2x4s flat over the foam running vertically up the roof,  24" o.c., screw down through all into the deck below (and the frame where I can hit it)

-  New plywood sheathing over the 2x4s, leaving a vents in the eaves and peak for air circulation.

-   New asphault shingles over the whole thing, ice and water where required.

Here are some questions/concerns I have:

-  Any problemss with the overall plan?

-  Condensation - since winter use (and therefore heating) is minimal, I doubt this will be a problem, but I can't be wrong and have my frame deteriorate.  Any comments?

-  Type of foam?  I'm looking at Foamular XPS - durable, little R loss, 25 psi compressive strength.  There is a Foamular product called Thermapink for uses in roofs, can take higher heat, but is really designed for flat roof membranes right on top of the foam.  Do I need this?  My experience leads me to believe that regular 25 psi would be fine with the vent space above the foam......

I greatly appreciate any helpful comments or advice you might have.   JVS

[Brian_Weekley]

Planning to return to Maine this coming weekend to finish the roof on my timber frame before the snow flies.  Thought I'd share my final plan of how I'm going to insulate and roof it...

http://youtu.be/DclbGgw1GqE

If all goes well, I'll post some actual photos when complete.

[Satamax]

Brian, what kind of thickness? What type of insulation?

Thanks a lot.

Max.

[Brian_Weekley]

4 inches of polyiso (2 layers of 2 inch, staggered seams).  Could be more, but should be adequate for a small workshop that will only be heated on occasion.

A few more details:

The "blue" strip at the bottom represents the bottom vent.  I'm using the Cor-a-vent S400 at the bottom behind the fascia and the V300 at the ridge.  This will enable air flow above the insulation and below the 5/8 sheathing.  I opted for sheathing on top of the strapping to create the "cold roof"--mainly because the manufacturer recommends the 5V crimp metal roofing that I'm using to be installed on solid substrate (doesn't have to be, but preferred).

[Stephen1]

Thanks for all the information to consider.  Here's one thing I'm struggling with:  I typically think of using a thin coating of spray foam on the inside of walls/ceiling to primarily eliminate air infiltration.  However, if I were to spray the underside of the roof decking (from the inside), it seems you would still have the concern of condensation from under the tin making its way down to the decking.  Therefore, it seems the most important thing is to have a good barrier under the tin and good airflow to keep things dry.  Do any of you folks have tin on SIPs?  What's keeping the condensation from rotting the top layer of your SIP panels?  Makes me almost think tin isn't worth the trouble with all these condensation/moisture concerns?  I guess there are advantages sticking with sheathing over polyiso, felt, and conventional shingles instead?

I used tin on sips. I also used tyvak house wrap to shed the moisture from the tin, then double strapped with 2x4 because they were used, crosswise to allow airflow. The steel salesman insisted on that before he would sell it to me. He had pulled tin off of sips due to rot from the moisture off the tin. I have the ridge cap that is open as well as the gable ends breath.
Be safe on that roof.

[Brian_Weekley]

I made a banzai trip to Maine for one final gasp to get the metal roof on before winter.  Day one was cold, but sunny and we got most of the panels on.  However, the second day was very cold with extremely high winds.  We really struggled just to stay on the roof and couldn't get the cap on.  I'm sure the folks driving by thought we were totally nuts.  Made one more attempt on day three and finally got 'r done.  Just in time too because it snowed the next day!  The style of roof I went with is the traditional "5V" in the plain galvalume color.  All in all, I think it came out pretty nice.













I know, we didn't use proper ladder jacks--don't report us to OSHA!

[WmFritz]

Got to be a good feeling to have it finished before winter.  8)

All your planning came out great. Nice job, Brian.

[thecfarm]

Just in time for the snow that is coming in.

[giant splinter]

Wow,
Just in the nick of time with the winter months ahead, you will be able to rest at ease for the next few months and plan ahead for your next phase of progress. Your project is moving along at a nice pace and looks very well built, on the subject of ladders ..... I do my metal roofing the same way and though the photos don't show it I would bet you anchored the base of those ladders in a very solid and dependably stable manner. In any case you have a good roof on just in time for the winter and no one slid off in the process, some one once said "its never the fall that hurts ---- it's the landing".
The roof looks great Brian and the progress is fitting together very well, stick with it and keep everyone up to date.

[Brian_Weekley]

I do my metal roofing the same way and though the photos don't show it I would bet you anchored the base of those ladders in a very solid and dependably stable manner.

Anchoring the base of the ladders is very important.  Large crowbars were driven into the ground until the crook captured the last ladder rung.