ptc@home 3: Rigid Styrofoam Insulation and Drainvent Rainscreen
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- Опубликовано: 22 авг 2024
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How to install two layers of foam and Tyvek's Drainvent rainscreen over an old, lightly-insulated wall
Now it’s time to wrap the home with Styrofoam insulation and Drainvent rainscreen.
Before covering the house with layers of styrofoam and Drainvent, I had a local insulator blow cellulose into the stud cavities, which added about R-13. Two inches of Styrofoam on the outside will bring R-value to around R-23, which is a pretty respectable upgrade for a sixty-year-old house in climate zone 5.
Beyond the extra R’s in the wall, the airtightness will be significantly better.
Exterior insulation should be continuous and airtight
I began installing Styrofoam at the corner with full sheets. It doesn’t matter if the sheets are vertical or horizontal, just make sure to offset the seams in the layers.
You don’t need to tape the seams on the first layer, at least that’s what veterans of the process tell me because taping the second layer’s offset seams will stop air movement. It’s also OK to use up scraps on that first layer, as long as they are tight.
The bottom detail uses coil stock bent in a j-channel shape to keep bugs out. Tyvel overlaps the upturned lag and the front is sealed to the foam with Tyvek tape.
The second layer of foam is offset from the first and the outer seams are taped. Again, it is important to tool the tape into the substrate to improve the adhesion.
At the top of the wall, I pieced in skinny rips to fill in tight to the soffit. When I tear off the roof next year, I’ll cut off the rafter tails and seal the roof/wall intersection with peel and stick membrane, sealing it to the Tyvek. The soffit and fascia will then be boxed out as illustrated in other Protradecraft videos and animations.
Under the window, I also had to piece in some smaller parts because whoever framed this house didn’t predict that I’d be using full 4x8 sheets.
I trimmed the edges under the window on an angle so that the sill flashing would slope outward.
Speaking of sill flashing, The window sill flashing should extend outside the foam to kick any water getting into the outside of the wall.
This outer face of styrofoam is effectively the WRB and drainage plane for leaks, so overlap the tapes and flashings correctly. And wet the adhesive into the substrate with a squeegee or j-roller. You can see that I goofed up and forgot to tape that far corner before sticking the flashing tape to the foam, but I was able to recover and tuck the tape behind the FlexWrap.
As always, it is important to tool construction tapes and flashing tapes to the substrate because the adhesives work best when mashed into the 3-dimensional topography of the substrate. Rainscreen allows water that gets past siding to drain out
With the foam installed and taped tight, I can add the layer of DrainVent rainscreen to the outside.
Rainscreen creates a drainage space for liquid water to drop through so that it is not held tight between the siding and the WRB. This extends the life of the siding and improves the durability of the wall system. Drainvent is an entangled mesh product that allows air movement in all directions, unlike using furring strips, which restrict air movement to up and down.
Again, with this sheet product, I tack the corners until I have the whole piece where I want it and then I add additional fasteners. Also like the Tyvek, I want to align the bottom of the sheet exactly where I want it to be, and smooth the rest tight.
I run the Drainvent over the window and cut out the excess afterward. I am still using the minimum number of fasteners because the siding nails will still penetrate all of the layers, too.
The second-row stacks atop the first with the mesh butting the previous course. There is no overlap. The outer fabric-y layer is protection against stucco or mortar from blocking the mesh. It is not a water barrier or an air barrier-all of that stuff is detailed already, this layer is just a spacer.
Detail the bottom of the wall to keep bugs out
At the bottom of the wall, the flap is tucked under the mesh to provide an insect barrier; the flap doesn’t really do anything in the middle of a wall like this, so just overlap it.. I actually trimmed it off and used it to wrap the edges of window openings for added protection against highly determined bugs.
That’s pretty much all there is to installing the Drainvent rainscreen.
Now we’re ready to put up some TruExterior trim and siding from Boral Building Products
Which I’ll do next time on ptc@home
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Always nice to see high-performance building techniques done in a “normal” and affordable way!
Thanks Tim.
That music is dope! Thanks for making this so informative and entertaining. Watching 2 years later.
Glad you enjoyed it, Kurt, I'm digging the zero energy bills!
Loving the music too!! Nice.
Thank you. We usually get complaints about the music.
Cannot wait to follow you through this project. I was looking for some local contractors that do this but none do. I will probably do it DIY on my own house.
It is astounding to me how many contractors do not know what this is. I have been covering it here on Protradecraft for seven years and was covering it at Fine Homebuilding for a decade before that.
It seems like malpractice to not know what the current science is saying about your product. I mean 17 years is a significant chunk of any career to not know what improvements were coming through the code cycles.
@@ProTradeCraftI have a house in MA. Can I do this to my house?
Styrofoam off gasing is 1500 times as bad as CO2 regarding GHG's. Please use rigid mineral wool AKA Roxul comfort board
Agreed that m,ineral wool is better for GHGs. Styrofoam now has a zero GWP rigid insul;ation, which you can see in the forst episode of Building Resilience season 3
Could you elaborate on your window flashing detail? I saw you had a typical peel and stick flashing under the window and tied into your tyvek layer. However after the rigid foam was added, it looked like you added a second flashing that overlaps the foam, but how is it installed back to the window? Is it just run up against the window and adhered over the first flashing? Or does it get lapped under the first window flashing somehow, layered like shingles?
A little bit of both, depending on what your wall looks like. If the windows have already been replaced, you can not tuck it under the window.
Sealing the Tyvek is more for air sealing than water management at that layer.
The second layer is water management, extending from the window out over the foam.
Hope that helps.
I'm sure I'm not understanding something, but isn't the Styrofoam impermeable to air and water? Doesn't this mean that any moisture from the inside of the house will go through the Tyvek house wrap but hit the Styrofoam and get trapped?
It is basically impermeable to air and moisture, and the thicker it gets, the more impermeable it is.
So, yes, moisture from inside could find it's way to the backside of the wall sheathing and diffuse through it to the backside of the Tyvek, diffuse through that and hit the backside of the foam.
However, according to physics, moisture goes from more to less, so unless it is very wet inside, the moisture will likely dry back inward. If it is THAT moist inside, an exhaust fan is certainly in order.
The more important piece of that equation, though, is that the vast majority of moisture movement is on air currents, NOT through diffusion. So, with a good installation of the Tyvek and Styrofoam, there ought to be very little air pushing its way through the wall system.
yes! that is what I thought too! House needs to breath??
In Tyvek installation guide it says 1. Tyvek wrap. 2 Foam Insulation. 3 Tyvek rainscreen wrap. 4 Cladding.
But I guess it fine like this.
There are a bajillion options in the tyvek manual. The detail here was developed in partnership with the Tyvek technical department because it represents one of the scenarios they did NOT already cover.
Love your stuff! Thanks for sharing. Curious...anti-racist but pro marxist?
Glad you like It. ✌
If water gets through to the backside of the insulation (maybe through your window bucks), are you concerned with it at all getting trapped in your coil stock at the bottom?
No. The coil stock bug protection is taped tightly to the face of the Styrofoam
Where does one acquire the metal channel?
Bend it from coil stock on a sheet metal brake.
Haha so I can copy and do exactly this in Massachusetts?
Pretty much. This house in in North CT
Is it okay if I don’t have continuous insulation into roof and on basement foundation?
Yes, but continuous is better. On this house, I just did the walls, not the roof, and it reduced energy use by at least 40% right off the bat.
What siding doesn’t require furring strips over 2” of foam board?
siding with long nails.
@@ProTradeCraftHi there thanks for taking the time to make a video on your project. Question:
Do you think installing drain vent rainscreen over poly iso (astm-c1289type2 class1 grade1)with Compressive Strength of 16 psi be an issue if HardiePlank will be nailed through both layers ? if yes would (grade2)20 psi work ? correct me if Im wrong the product you are using is 25 psi compressive strength ? Im worried about hardiplank being wavy when compressing drainvent to rigid insulation. I like the idea of having a gap between the siding and the rigid insulation without having to nail furring strips.
The house your working on in the video... what is the main source of heating ? electrical baseboards or forced air natural gas
Did you add any makeup air or HRV/ERV when project was complete ?
I ONLY COME HERE FOR THE MUSIC...
YOWSA!
Stay for the comedy!
That siding will fall off! He didn’t hit any studs and that so called bug screen will get dust in it and prevent airflow
Disagree. The wall sheathing is 3/4 inch solid lumber, and almost all siding products are rated for 7/16 OSB.
Not sure where all the dust id going to comer from hiding behind siding, but...
What's your preferred system for exterior insulation and rainscreen?
1:15 where do you get details like that?
From a LONG career in construction and construction media.
That base of wall detail is one I've been covering for decades through Fine Homebuilding, GreenBuildingAdvisor, and now Protradecraft.
I worked out all of the details with DuPont's Building Knowledge experts as well as some top-notch builders/remodelers.
The helium-using person talking in the background was distracting.
No helium balloons were injured in the making of this video
Terrible music choice.
HA! see comment above!
Thank you.