Anyone used Tyvek DrainWrap?

Do I need a vapor barrier on the inside walls of my SIPS home?

Thanks

no. the vapor barrier goes on the outside. This way the moisture can drain outside the building. If you provide it on the inside it will create puddles on the floor like a refrigerator that has no where for condensation water to go.

Note there are a lot of different types of drain wrap for different applications like stucco or siding. Make sure you use the one that is acceptible for the job and the site as approved by your building inspector. Removing siding or stucco will be very expensive if you get red flagged by an inspector.

Tyvek has become very popular and I am not sure why. Felt paper has been around for years, is proven effective and is much less expensive. I still use it.

A vapor barrier isn't needed on a SIP wall at all. The Permeability (moisture transfer) of a SIP wall is very low; therefore the the panel is the vapor barrier. If you did put something up on the inside I doubt there would be any issues, especially puddling?? The barrier would have to have one side exposed to cold temperature for condensation to occur; which doesn't occur on a properly installed SIP wall.
Now the exterior is another issue. You need a house wrap to protect the sheathing from moisture getting behind/through your siding. You would think tar paper would work well in this capacity; you would be wrong! If moisture laden interior air escapes the housing envelope, which isn't uncommon, you want something that is permeable. Otherwise there will be condensation beneath the layer of house wrap, which will be absorbed by the Exterior OSB skin. Thats why housewraps are designed to keep rain out, but let humidity pass through.

srs22,

Can you provide some more details for your conclusions? I believe that most of your concern probably comes from penetrations which will obviously be a source of concern. But if a wall or roof for that matter is sealed and has proper HVAC, there shouldn't be an issue with moisture from the inside of the house. If it was then you would think there would be code that requires a permeable layer between the felt and the tar on the roof. My best guess is that the house wraps were designed for poor stick construction and should not be necessary with a tightly sealed home like those found in SIP construction. And if there are studies out there indicating the need for house wraps (other then felt) on SIP homes I would hope they be conducted by independent companies without benefit from the wrap manufacturers. In some ICF construction, stucco is applied directly to the exterior of the house skipping the wrap and lath. Wouldn't this suggest that the true issues of outside moisture and installation be of concern rather then the issue of inside humididty?

My local codes (northern midwest) require a vapor barrier on the inside walls of the house. The idea is that this prevents the moisture laden air from the inside from migrating through the walls during the winter to condense on the outer sheathing.

The need for and location of a vapor barrier is a subject of many disputes and the climate in your area is certainly a factor. I would consult with your SIP manufacturer for their recommendations for your climate and then confirm with your local authorities to see if the SIP manufacturer recommendations meet your local code.

If you do a search you will find many opinions.

greg,

Do you have any information on this requirement for SIPs? If moisture could pass through foam then it wouldn't float.

Regardless of how well your HVAC system functions and you monitor indoor humidity levels you will still have a large temperature differences from interior air to exterior air (Cold climates). Humidity is measured by is relativity to temperature (relative humidity); therefore having the appropriate interior humidity level is still going to cause condensation as it escapes the insulated envelope and comes in contact w/a surface that is several degrees colder.

House wraps were more then likely designed for "leaky stick framed" structures, but a product that repels water and allows water vapor to pass is a friend for any cold climate wall assembly.

Again the tar paper works in theory, but anywhere interior air escapes, there will be condensation behind the tar paper in the winter months. An argument can be made about "tightly sealed SIP construction"; there is truth to this, but again you'll never make the envelope air tight. I've sat in on several blower door test, of our SIP homes and conventionally framed structures. The SIP structures perform considerably better, but certainly not air tight. Until they make panels with a water repellent exterior, you'll need a moisture barrier. For the cost increase (i would argue there isn't one) might as well use something that will handle the water vapor accordingly.

There are still building departments that require interior vapor barriers. This is outdated and in my opinion incorrect. Any moisture that does get into the wall cavity (leaks around openings, wet when built, etc) will never dry out.

.... They do make water repellent sips   Steel SIPs!

Your right.  Steel SIPs shouldn't need an exterior house wrap.  Obviously you would want to verify this w/manufacturers specs, but I not sure why they would need any additional barriers on the exterior.

mm - it's just what my county requires regardless of the wall construction. The only way around it would be if the SIP manufacturer could provide data showing the completed inner surface functions as a vapor barrier (including joints). I don't agree with the inside vapor barrier for all cases but they didn't ask me! LOL

As far as moisture through foam I have no idea if SIP manufacturers have data to show that moisture VAPOR cannot go through their foams. Perhaps they can produce data to show vapor transmittance equivalence to 6 mil poly (what my county likes to see as a vapor barrier). I do know that some materials will float because they will not allow liquid water to pass through but they will allow water vapor to go through . And in Northern climates it is the internal water vapor that can cause problems so a float test is meaningless.

As you said the main moisture issue with SIPs in Northern climates appears to be interior moisture vapor passing through joints and electrical openings if they are not properly sealed. I believe most manufacturers require the use of a special tape for this.

gregj;

 

I can guarrantee you will never get water vapor to pass thru a sheet of 26 ga. steel, the joints can be caulked or taped.

We use exposed steel panels for the finished roof on simple gable style roofs. If it keeps out the elements it will certainly not allow moisture vapor to pass thru

Now that sounds pretty good. You just put adhesive between the panels, put them on the roof, and you're finished? No felt, no shingles? What about the connection at the ridge?

Jelly;

Steel ridge cap

Hi I am new to this forum but I have to say WOW what a wealth of information!!! My question has to do with Steel roofing use on SIP roof panels. Did I undestand correctly that Steel is used as the outside sheething of the panel? If so how would this work if I were to use this system for my roof panels? I am building a small home in the far northwestern suburbs of Minneapolis where we have had some very diverse weather conditions. Shouldn't there be an air space between the roofing system and the sub strate for ventilation of ambient moisture? And How about the ridges on the roof? How would they be sealed from the elements to insure that the moisture or condesate will not flow onto and eventually through the roof into the living space below? I have some experience with the use SIPs through a relatives home built a few years ago and there has been some issues with condensation leaking into the living spaces. Thank you for your time. Pauly

Chris,

So where does the water vapor go when it condenses on the inside of the steel?

Never had any condensate on the inside, there is no temperature difference on the interior skin and the surrounding air, so it wouldn't condensate any more than a metal cabinet or an metal appliance on the interior space............. the panels are furred out with steel hi-hat furring (for wire chase) then covered with 1/2" drywall.

As with any tight building envelope, ICF, OSB or Steel SIPs it is recommended that you install an Air exchanger or heat exchanger depending on your climate to extract moisture and introduce fresh air

Pauly;

Steel is on inside and outside skins of Steel SIPs

ridge gets a steel cap to keep weathertight

Joints are taped for water-tightness

The OSB sips that your relatives had a problem with were not sealed correctly or the splines may have shrunk to allow air to get thru

I was referring to the inside surface of the exterior steel skin which you say serves as a vapor barrier. Up north here moisture vapor from inside the house would keep migrating out until it either hits a vaopr barrier or it hits the dew point and condenses. So our interior vapor prevents it from reaching that point in the insulated wall where the temp is at the dew point. But then your interior steel skin also serves as a vapor barrier too I guess. Down south you have the opposite conditions where the hot humid air is on the outside working its way in to the dew point of the cold air conditioned walls so an exterior vapor barrier is indeed what you want.

I thought a double vapor barrier(interior and exterior) was a no no as any water intrusion that might occur can never dry out. I suppose if you can guarantee that no water can ever get into the SIP then it's ok.

gregji;

 

There is really no where for water to get trapped inside the panels, they are a solid core

Example: steel insulated door panels are a smaller version of a steel SIP. I had them on my home when I lived in Pennsylvania and never had condensation even at 15 below

This discussion is a little old, but I would like to add to the topic.

Depending on the climate and where the temperature and humidity differential is, a vapor barrier is very important regardless of building material used. Air exchangers and other mechanical means of keeping the correct environmental balance are by their nature dynamic systems and therefore dependent upon the building occupant for correct operation and performance. Static controls, IE vapor barriers and well designed and constructed building envelopes are static systems and will perform properly for the life of the structure.

SIP construction and the need for careful assembly and good vapor barriers is demonstrated by the Juneau, AK failures. Although the failures occurred in the roof, I personally believe a complete and carefully executed interior vapor barrier in concert with a properly maintained HVAC system is the best approach. I invite you to read the material found at the following links and then draw your own conclusions.

Sincerely,

Coppcar

http://www.sipweb.com/2001-10_juneau.pdf

http://www.sips.org/content/technical/index.cfm?PageId=161

http://www.juneau.org/cddftp/bldghandouts2003/SIP_ROOF.pdf