Need some advice in my renovation

[Drewski123]

I have listed some of the options / ideas of what I am going to do with each part:

1. Bathroom Ceiling:
Option1:
• 5/8” greenboard
• 6mil plastic sheeting
• on attic side, greenfiber blow-in up to a recommended amount to achieve a high R-Value

Option2:
• 5/8” greenboard
• Faced Fiberglass Insulation Batts (faced down toward the bathroom ceiling)
• On top of batts, greenfiber blown-in to a recommended amount to achieve a high R-Value

Which option would make more sense?

2. Exterior Wall (will have no fixtures / no running pipes, just a window)

• Ultratouch batts
• 6mil plastic sheeting
• 5/8” greenboard (for better insulation)

3. Tub/Shower wall surround:

• No insulation in wall cavities
• 6mil plastic sheeting
• ½” Durock
• Shlutzer Kerdi membrane
• Tiles


4. Also, I will be insulating a garage ceiling, so our bedroom (which is directly above this unheated garage) will be much warmer in the winter months.

• About 2” of insulated sheathing (like XPS, EPS, or Polyiso, etc.)
• Ultratouch batts
• 5/8” Type X Drywall

In terms of insulated foam sheathing, I am not sure which one would be best for this project. Should I use boards that contain laminated facers on both sides, on one side, or neither, just “unfaced”? Should I use XPS, EPS, or Polyiso?

Please, advice / comment on all of these above points.
Thank you.

[jadnashua]

There's no reason for greenboard on the ceiling...regular drywall is actually stronger, and with a good coat of primer and paint, just as good (actually, the greenboard can droop, whereas the drywall is not likely to).

Where you are adding Kerdi, you don't want another vapor barrier on the wall - this would allow moisture to possibly be trapped between them - only one on any one wall.

[Drewski123]

Kerdi will be applied only in the wet area (shower/tub area).

[Dana]

Blown insulation works better than batts in every real world situation, even when they're equivalent in a lab. Cellulose is a good $/r value, and is a much better air-retardent than low-density fiberglass. In the attic dry-blown is fine, but insist upon "borate only" or "sulfate-free" material (IIRC Greenfiber is still using sulfated fire retardents in their dry-blown product.) All wet-sprayed or "stabilized formula" cellulose is borate-only. Aluminum sulfate can corrode metals if it ever gets wet, but on the upside you'll KNOW if it gets wet by that "eau du cat" litterbox smell. Batts are NEVER installed perfectly, and every void/compression creates a thermal leak and a potential moisture issue.

Also, cellulose protects the structural timber from seasonal moisture drives by wicking & buffering the moisture, something that mineral or glass-fiber products can't do. (Cotton does this as well, but it's more expensive.)

There's no excuse for using true vapor-barriers such as 6mil plastic or metal foil is in a Seattle climate- it's a "solution-problem", that limits wall assembly to drying only to the exterior, and unless you've built the interior-side to be truly air-tight (caulked & gasketed everywhere, blower-door tested) it'll be more likely to trap moisture that gets into the wall/ceiling via air-leaks than it is to protect the sheathing & stud. On the walls, as little as 3/4" of exterior XPS is sufficient to keep the sheathing above the average interior dew point during the coldest months in which case you need nothing more vapor retardent on the interior than standard latex. see: http://www.buildingscience.com/docum...r-requirements Seattle is in marine zone 4.

With exterior rigid foam the ability to dry toward the exterior is compromised (foil faced goods are more vapor-retardent than 6 mil poly), making keeping the interior side at least semi-permeable even more critical. Concentrate on making the wallboard layer air-tight, caulking as you install it and foaming any electrical or plumbing penetrations, and keep the wall/ceiling as vapor-permeable as latex paint will allow- it'll be far more resiliant to moisture that way.

From a thermal and moisture performance point of view the type of foam used is far less critical than it's R-value relative to the center-cavity fiber's R value. Iso (polyisocynurate) will give you more performance per inch of thickness in a Seattle climate, but XPS isn't far behind. From a total greenliness point of view iso and EPS are more benign than XPS, since they use pentane as the blowing agent rather than the HFC-143 commonly used for XPS, with but a fraction of the greenhouse ozone layer environmental burdens.

Both EPS and XPS gain R with falling temps, being 5-10% higher in R at a average temp of 25F than at 75F number, whereas iso falls by a bit. If your mean January temp was below 25F instead of nearly 40F derating the iso to R5.6/inch down from R6/inch and up-rating EPS from R4/inch to R4.4/inch would be in order but in Seattle you can assume the performance of exterior foam to be pretty close to it's labeled R-value.

Kraft facers on batts are about ~0.5 perms (compared to 2-3 perms for latex paint), and can't be relied upon as an air-barrier by themselves.

Using 1/4" fan-fold XPS siding-underlayment can be used between the gypsum/tile-backer and studs/joists around the tub makes for a ~0.75 perm vapor retarder (about the same perm-rating as Kerdi) and capillary break, an order of magnitude preferable to 0.03-perm 6-mil poly It keeps the peak-event moisture from showering/bathing out of the assembly, but still allows it to dry toward the interior the rest of the time.

[Drewski123]

Dana, in regards to insulating an unheated garage ceiling, so our bedroom (which is directly above this unheated garage) will be much warmer in the winter months, can I use 1.5” XPS (or EPS) rigid insulation as a first layer, then add Ultratouch batts (8" thick), and lastly 5/8” Type X Drywall?

Is this combination going to work? Should I use faced or unfaced rigid boards?

Thanks for your help,
Andy

[Dana]

Batts are kinda crummy from a total performance point of view, since they have to be installed PERFECTLY to achieve rated performance. Blown fiber fills in everywhere, even the gaps between the Romex and the edges of the drill holes where it's routed through joists or studs.

Facers on rigid foam are almost always low-perm vapor barriers, and unless there's a reason to put one in the stackup, you shouldn't. In a heating dominated climate it's better to put the most vapor-retardent element on the interior side of the assembly, but if it's on the exterior, as long as there's sufficient R value to the exterior of the vapor barrier that it's average temp in the coldest weeks of the year stays above 40F, you'll be OK, so long as there's only one vapor barrier (less than 1 perm) element in the stackup.

So whether you can use foil-faced rigid foam on the garage side of the stackup depends on what you have for a finish-floor & underlayment. Asphalt tile, vinyl flooring etc are very low-perm, but would be on the "correct" (warm-in-winter) side of the stackup, but would mean you should avoid putting faced goods on the bottoms of the joists. Hardwoods, rugs, ceramic tiles etc are vapor permeable, and not a problem, as long as you used rosin-paper rather than 6-mil poly or something as the slip surface between hardwood & sub-floor.

But no matter, the garage is semi-conditioned space, and the garage itself will likely average well above 40F even in January, so build it out without faced rigid foam and you'll be fine. Something like this will work:

Finish floor .
sub-floor .
blown cellulose, full cavity fill
7/16" OSB .
1-3" EPS (or 1-2" XPS) .
1/2"-5/8"gypsum .
Standard latex paint

If you MUST use batts, make sure that it's a full cavity fill- an air gap between the subfloor and the top of the batt is thermal-bypass, it will lower the as-installed R value of the batt due to convection, and any air-leakage at the ends can & will travel unimpeded through the joist bays, chilling the floor. If it's 2x10 joiste, low density unfaced fiberglass R38s snugged up to the subfloor and compressed compressed, would be "good enough", and would perform better than an an 8" Ultratouch with an air gap on one side or the other. If there must be an air gap, make it on the garage side of the assembly. (But blown goods are really the way to go here. It's not rocket science to get 2.5lbs+ density out of a rental blower even without dense-packing hose.)

[Drewski123]

Thanks Dana.

I have purchased batts already so I need to use them.

So here are the final layers:

In the bedroom:
Existing finished floor (hardwood)
Exisitng sub-floor 7/8" tongue and grove + a layer of paper (some kind a light brown paper) + 5/8" ply

In the garage's joist cavity (joist cavity is 9.25"):
Adding Ultratouch batts (R30) 8" thick
1.5" EPS (XPS)
5/8" Type X gypsum
Standard latex paint

The joist cavity should be totally filled in without any voids. The batts are 8" thick, plus 1.5 EPS (or XPS) would add up to 9.5". In this case the batts will be squeezed in by 1/2".

Also, you listed EPS/XPS as a last layer before installing drywall. Is there a reason for this? Can the rigid boards be installed first in the cavity, and then the batts?
And lastly, you mentioned 7/16" OSB. What is this OSB for?

I appreciate you help Dana.

Andy

[Dana]

If you put the rigid board in the cavity, it's R-value is undercut by the thermal bridging of the joists. A 9.5" joist is about an R8-8.5 thermal short in your othewise R30+ floor. If 16" on center that will end up being well over 10% of the total floor area (counting blocking & other framing), and a large fraction of the total heat transfer between the garage & bedroom. If you instead put the foam on the exterior of the joists you're adding the full R of the foam to that thermal short. A 1.5" layer of XPS is R7.5, which is effectively cutting the framing losses in half. By thermally breaking the framing you boost the thermal performance of the assembly by more than 20% using the same amounts & types of materials. Putting high-cost per R foam in framing cavites is usually a waste, since it can be used more effectively as a thermal break outside the framing.

It's also more work, with more foam scrap to cut'n'cobble the foam into the cavities.

The purpose of the OSB would be there to guarantee that the recommended 2.5lb+ cellulose fill would not warp the gypsum over time, since it will be under pressure at that density. If 16" on center 5/8 gypsum + 1.5" of XPS should be stiff enough for 2.5lb cellulose, but installing the cellulose would involve drilling 2.5-3" holes in it to and snake the hose into the cavity, and you'd have to plug & finish the holes later. You could use a blown-in-mesh approach, but finding the right mesh is more than a trip to the box store, and the minimum roll would likely be several times what you'd need.

If going with a batt solution the OSB can be skipped. Stagger the seams of the gypsum with that of the foam for better air-tightness. To be even more serious about air sealing (and I would be) caulk the foam seams as you go or use housewrap tape over the seams and caulk the edges where it meets the wall before putting up the gypsum.

If using batts, see if you can't find a source for un-faced R7-R8 econobatts (used in 2x3 framing), or alternatively you could split unfaced R19 and compress it into the 1.5" gap. Compressed to 1.5" it would add another R5-6 to the center-cavity R, but the more important aspect would be that it retards the thermal bypass and convection currents that robs fiber insulation of performance.

[johnfrwhipple]

...Where you are adding Kerdi, you don't want another vapor barrier on the wall - this would allow moisture to possibly be trapped between them - only one on any one wall.

Careful following this advice. A vapour barrier is most likely required by code and will be part of your inspection process. Kerdi does not provide a proper vapour barrier in most builds we see. If you can tie it into the remaining vapour barrier you will be OK but this is very difficult and will deviate from Kerdi's install guidelines most likely.

If you call Schluter they will tell you its OK to use both. This moisture sandwich issue is one that cause much confusion online and one we struggle with on a regular basis.

On an exterior wall we prefer the use of a liquid membrane over your cement board - the liquids can allow trapped moisture out and stop it from getting in. Cement board will allow moisture to migrate uo and out if the wall is not fully waterproofed. We water proof our showers and tub surrounds to 6' above grade - since an average wall is 8' you have a 2' breathing space.

Check with your local building department as to your cities requirements - here in Vancouver the inspectors want to see 6mil VB before you even break out the cement backer board.

You'll find that liquid membranes are easier to install and cost less too!

Good luck with your renovation.

JW

[Drewski123]

John, I decided to use Wedi boards instead of Durock with Kerdi membrane. The tub/shower alcove is not on the exterior wall. Do I still need a vapor barrier behind the Wedi board which would be installed right to the studs (The Wedi board is waterproof)? Also, you mentioned that in Vancouver, the inspectors require 6mil vapor barier. Since Vancouver and Seattle have similar weather, do you think that this requirement applies to Seattle as well? I will call the building inspector on Monday to make sure I will be doing this correctly.

[johnfrwhipple]

I have not worked with Wedi board before but understand it to be very similar to Kerdi Board. In fact Wedi Board has been around much longer than Kerdi Board and has a longer proven track record.

Vapour barriers are only required on exterior walls and not so in a tub surround. Your weakest connection point will be the very bottom of the Wedi Board where it meets the tub deck. I should just point out as well that a vapour barrier is required in your ceiling if it is the top floor.

If you install a solid blocking course at the tub tile flange elevation you will be able to insure no flex at this point and get some of the Wedi Chaulking to seal this connection.

I have found that Kerdi Board will wick water if the ends are not banded and would imagine that Wedi might do the same. Take care with this connection point and you should have a bullet proof install. I would contact a Wedi Tech to ask the best method of insure no water makes it way under the Wedi Board at the tub deck connection point.

Good Luck.

JW

[Dana]

John, I decided to use Wedi boards instead of Durock with Kerdi membrane. The tub/shower alcove is not on the exterior wall. Do I still need a vapor barrier behind the Wedi board which would be installed right to the studs (The Wedi board is waterproof)? Also, you mentioned that in Vancouver, the inspectors require 6mil vapor barier. Since Vancouver and Seattle have similar weather, do you think that this requirement applies to Seattle as well? I will call the building inspector on Monday to make sure I will be doing this correctly.

A 6 mil vapor barrier on all exterior walls (including basements) is part of the Canadian national building code, but it makes far more sense in Winnipeg where for 3 months of the winter the interior side of the structural sheathing of a studwall stays below the dew point of the inteior air, than in Vancouver where even the exterior of the siding (the great outdoors) average dew point is at or above the dew point of interior air except during extended cold-snaps. If the wall is built with Canadian code-required 10mm rainscreen under the siding the drying capacity of the sheathing is enhances, and merely painting the interior wallboard with standard latex paint is sufficient vapor retardency to protect it in Vancouver, but Calgary, Winnipeg or Montreal would either need the 6mil poly, sufficient exterior foam, or gypsum/fiber-cement/other structural sheathing less susceptible to and more vapor permeable to moisture, even with the rainscreen. Whenever condensation control is possible WITHOUT poly or foil vapor retarders, the resulting assembly will be more resilient to construction errors (minor air-leaks, etc.) since it's ability to self-purge moisture will be dramatically higher. In Seattle or Vancouver climates that should be easy (were it not for pesky inspectors less versed on the building science behind IRC 2009. :-) )

As long as the bathroom meets code on ventilation, in Seattle a 0.5-1 perm vapor retarder (or 0.75perm Kerdi) will be sufficient moisture protection from interior vapor drives, independently of the wall stackup. The air tightness of the vapor barrier layer or interior wall is orders of magnitude more important than it's absolute permeability, and a 6 mil vapor barrier that isn't air tight will raise (not lower) the risk of moisture accumulation in the sheathing or studs, since air-transported moisture that gets into the assembly has a much harder time getting out via vapor permeation through ~0.05 perm poly. Detailing the Kerdi/other as well as the interior finish layers to be air-tight is the "right" way to go.

SFAIK interior vapor retarders as severe as poly are not required by code in Seattle, but depending on the wall stackup including insulation, sheathing, & siding types a sub 1.0-perm vapor retarder can still be useful. (1.0 perms is still more than twenty times the drying capacity of poly, Kerdi has more than 15x.) If it's 2x4 with even a half-inch of XPS would be sufficient to allow even 3-perms on the interior side. With unfaced UltraTouch batts the wood is somewhat further protected from the high moisture drives during showers by it's significant moisture buffering capacity taking up that moisture instead (similar to cellulose, in that regard), as long as the assembly is sufficiently vapor permeable to allow that moisture to dry for the other 23 hours of the day.

[johnfrwhipple]

I will interested in what the inspector has to say.

I read an article in Tile Letter this month that talked about steam showers and Perm Ratings. The article was suggesting a perm rating of .15 for commercial jobs and .50 for residential. I was glad to read this since I work with Nobel TS for my steam shower projects and the Perm Rating is 0.05 - head and shoulders above Kerdi at 0.75. If these new recommendations come to be Kerdi will need to be fully re-engineered.

Even with a higher Perm Rating that Nobel has it is still a hard task to tie it into a homes vapour barrier system.

My home has a ran screen and my master en-suite shower has three exterior walls. I used some 6mil poly and then Concrete Board. I will use some liquid waterproofing product over top. This will not be a steam shower.

I would have thought Seattle and Vancouver would have similiar building codes???

When I designed the Earthquake aspects of my home I went for California Code over BC because theirs is better - I wonder if Seattle's codes trump that of Vancouver's???

JW

[Dana]

If Seattle has fully adopted the IRC 2009 climate-dependent moisture control & vapor retardency portions Seattle codes probably do work better than Vancouver's for some things, but less so for others. As I understand it Vancouver (as in all of Canada) requires a 10mm rainscreen gap under siding, whereas in Seattle that's completely optional (and rarely done), and the difference in drying rates toward the exterior is huge. But in Vancouver (as in all of Canada) a 6-mil poly vapor barrier on the interior is mandatory, which completely blocks drying toward the interior, in a climate where even in January the average temp of the sheathing will be well above the dew point of the conditioned space air, with the vast majority of winter hours favoring drying toward the interior.

In Vancouver with a 10mm rainscreen in place, keeping the interior more vapor-open (up to ~ 2-3 perms) rather than using 6 mil poly on the interior results in lower moisture content in the exterior wall framing and exterior sheathing- the assembly dries rapidly in both directions, and PLENTY rapidly to keep up with modest amount of time the sheathing spends below the dew point of the interior air. (Easily confirmed by a WUFI simulation of any number of stackups.) In Seattle without a rainscreen or exterior foam to keep the average temp of the sheathing high enough all exterior walls do better with a 0.5 perm or lower interior side vapor retarder. That slows but doesn't completely kill interior-drying capacity. Kraft facers are ~0.4 perms, and work fine if you keep it air-tight on the interior side. Poly works too, but makes the assembly less resilient by fully blocking drying to the interior. With rainscreened siding & 2 perm interior, drying times (even from bulk-water intrusions) can be remarkably short, and the risk of mold/rot become extremely low.

Placing 6-mil poly on interior walls that are kept vapor-open to the far side of the wall (the interior of the adjacent room) should not present a problem, and could only help. It's the exterior walls with fiber insulation that are most-susceptible though, since much of the winter the cool edge of the studs and the exterior sheathing will be well-below the dew point of active-showering dew points. But unless you're showering 3+ hours/day it's still not going to NEED to be below 0.75 perms, even without an exterior rainscreen to enhance drying capacity. (In a steam shower, maybe, or in public/commercial showers with high usage rates.)

[johnfrwhipple]

Drewski how are things shaping up? Did you visit with your inspectors?

If you can please share your findings with us as this information will help others in a similar boat.

Thanks,

JW