I have a question that I can’t seem to find an exact answer to due to a few extenuating circumstances. Any advice would be appreciated. I am in the midst of remodeling the exterior of my home(a ballon framed two family built in 1901 that doesn’t have a square or plumb wall in it). When I replaced the windows five years ago the old windows were so rotten I couldn’t use replacements, so the windows were removed,the framing repaired and new construction vinyl double hungs were installed. The house has cedar shakes with a 1/2″ layer of EPS and vinyl siding over them. To have a solid surface I used 1″ furring strips to reach the plane of the cedar shakes, nailed the nailing-fin to those and then ran the vinyl siding into the factory applied j-channel. NOW, here’s my question: I want to strip the exterior to the sheathing and replace it with 1″ XPS and finish with vinyl. Because the windows are furred out from the sheathing 1″ already this will put my siding back on the original plane with the j-channel. But I won’t have room for vertical furring strips to provide airflow behind the vinyl. Is this a problem? The house has r-11 in the walls but is still very drafty and I have concerns about condensation forming. Also would the XPS go over the housewrap or under it? I called Tyvek and they said either was acceptable. Opinions? Thanks in advance for reading this lengthy soliloquy and any input offered, and if I can help anyone out who needs advice about how to go broke remodeling your house while making it look good to your wife e-mail me. I have all the excuses cataloged alphabetically or in order of importance. TIA
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There's about 50 million houses in the US with vinyl siding that do not have the rainscreen detailing that I think you are describing. While it might be a great detail, you'd have to move your windows out to accomodate (as you are well aware). If you were to decide to move the windows, you might as well beef up the XPS to 1.5 or 2". Alternately, you might consider using Pactiv's Greenguard housewrap instead of Tyvek. It has vertical ribs that are supposed to channel water down. This would go over the XPS of course. This would allow you to go with the 1" and leave your windows intact.
Tyvek has a stuco wrap that will provide drainage behind foam board.
Why do you want to replace what you've got? How will getting rid
of the shakes increase your airtightness? I don't think the mere substitution of one inch of XPS for a half inch of EPS will make much of a difference in terms of airtighness or insulation value. But
if you are going to do that, why not use one inch shiplapped
polyiso and get more insulative value?
Secondly, I do not know how much of an rainscreen your climate
requires (if any) but a rule of thumb I have heard is 3/8".
Some people do it with coroplast strips rather than wood.
He is adding a house wrap along with the foamboard. If the house wrap and foamboard are both taped correctly, he will tighten up the old place considerably.
Thanks for the reply. The styrofoam I have currently is not the typical 2x8 foam. It looks very similar to double 4 lengths of siding, including the offset. I guess it was made to fit tight behind each course of siding. I thought that by stripping the house to the sheathing(because I want to change the vinyl siding anyway) that the modern sheets would be tighter than what I have. Also, I see some posts recommend taping everything. Tyvek was adamant that with XPS over tyvek that nothing be taped. Maybe I got some bad info from their factory rep. My main concern is condensation forming in the walls or sheathing because the inside of the house is loose. Its already sheetrocked so I can't do much about that now. I've read about the importance of vapor barriers and I'm concerned that with the insulation job that was done, (craftfaced r-11 batts) the vapor barrier might not be sufficient. Thoughts?
"Tyvek was adamant that with XPS over tyvek that nothing be taped."
That's because you're creating an exterior vapor barrier and a potential condensation plane outside your sheathing and taping the housewrap would prevent any possibility of drainage. Taping the XPS would likewise prevent any vapor movement outward.
"I'm concerned that with the insulation job that was done, (craftfaced r-11 batts) the vapor barrier might not be sufficient."
It's highly likely that there is an insufficient vapor retarder or air barrier on the inside, so placing a vapor retarding membrane on the outside of the wall system is asking for trouble unless you take measures to air-seal the walls very well, allow for drainage and breathing outward, and keep the indoor relative humidity under 40%.
With the wall system you're describing, the inside of the sheathing would be 41° on a 30° day (with 65° indoor temp) - cold enough to condense. On a 0° day, it would be 21° - cold enough to condense and freeze.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 2/14/2008 6:45 pm ET by Riversong
Riversong, Thanks for the info. This is exactly what I was looking for.
Do you have any recommendations for this scenario?
I will also do some research on the building sciences site.
One other thing: As I've stated, my concern with the thickness of insulation under the siding was to hopefully put the vinyl siding back on the same plane as the j-channel which is integral to the windows. I imagine I could use 2 inch foam and then flash back under the j-channel if I have to. Would that solve the problem of any potential moisture that migrates from the interior condensing on the sheathing? Thanks for all the help
hey... is your return key broke ?
<<<<
100904.7 in reply to 100904.3
Thanks for the reply. The styrofoam I have currently is not the typical 2x8 foam. It looks very similar to double 4 lengths of siding, including the offset. I guess it was made to fit tight behind each course of siding. I thought that by stripping the house to the sheathing(because I want to change the vinyl siding anyway) that the modern sheets would be tighter than what I have. Also, I see some posts recommend taping everything. Tyvek was adamant that with XPS over tyvek that nothing be taped. Maybe I got some bad info from their factory rep. My main concern is condensation forming in the walls or sheathing because the inside of the house is loose. Its already sheetrocked so I can't do much about that now. I've read about the importance of vapor barriers and I'm concerned that with the insulation job that was done, (craftfaced r-11 batts) the vapor barrier might not be sufficient. Thoughts? >>>>
100904.7 in reply to 100904.3
Thanks for the reply.
The styrofoam I have currently is not the typical 2x8 foam. It looks very similar to double 4 lengths of siding, including the offset. I guess it was made to fit tight behind each course of siding.
I thought that by stripping the house to the sheathing(because I want to change the vinyl siding anyway) that the modern sheets would be tighter than what I have.
Also, I see some posts recommend taping everything. Tyvek was adamant that with XPS over tyvek that nothing be taped. Maybe I got some bad info from their factory rep.
My main concern is condensation forming in the walls or sheathing because the inside of the house is loose. Its already sheetrocked so I can't do much about that now.
I've read about the importance of vapor barriers and I'm concerned that with the insulation job that was done, (craftfaced r-11 batts) the vapor barrier might not be sufficient.
Thoughts?
Mike Smith Rhode Island : Design / Build / Repair / Restore
Sorry.
Can you tell I didn't do well in typing class?
I will make it a point to properly format future posts. Your right, it's much easier on the eyes.
I will now scourge myself to make atonement for my error. Back in fifteen minutes:)
And again, Thanks to anyone who replied to my post. I really appreciate the help. Hope I can be of service if anyone has HVAC questions.
Mike,
At the risk of inviting ire for hijacking a thread -- why are you obsessed with short paragraphs and the use of the "Enter" or "Return" key? Is it so long since the average American has read a book (as opposed to information on a Web page) than American eyes are no longer able to read a four-sentence or five-sentence paragraph? Let's assume that the average attention span is not so short that paragraphs are considered challenging to our brains. These posts aren't novels by Henry James or Herman Melville. Please, stop dissing traditional paragraphs. They won't kill you.
martin... i'm not obsessed at all but after your first sentence, i stopped reading.it's too hard to separate the words .. so if you are trying to get people to read what you write, then you should think of the
presentationMike Smith Rhode Island : Design / Build / Repair / Restore
It's a pity. You might find some interesting paragraphs out there, if you were willing to stay with an author beyond a single sentence.
It is just the oposite.Most books have lots of white space.It is not the contents of the paragraphs. It is the layout.With something like a newspaper column I can see both side at the same time. But with a long paragraph on a big screen I keep losing the phyiscal place when I go from right to left.And it is specially bad when there are lots of numbers. Where I want to go back several sentence to see what is said earlier to what is in the later sentence..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Bill,
Shrink the window on your computer monitor; that way you can create any column width you prefer. My point is not that I have any problem with other people's choice of layout. If someone wants to create a long series of one-sentence paragraphs, I have no problem with that. I'm just urging people to be more tolerant of the occasional poster, including me, who was taught that paragraph composition rules are a little more complicated than "one sentence is the maximum." But hey -- if the community consensus is, we ignore every sentence except the first sentence in each paragraph, so be it. I guess I've been warned. But all of you following that rule may, occasionally, be missing content of interest (although not in this particular paragraph). Nuff said.
Edited 2/15/2008 10:53 am ET by MartinHolladay
Edited 2/15/2008 10:54 am ET by MartinHolladay
martin... i read constantly
here , we have an easy opportunity to make it more enjoyable for our fellow posters
all it takes is the ENTER key
or a break key
just be advised, i think you're going to continue to make it an unpleasant experience
for what ?
gimme a breakMike Smith Rhode Island : Design / Build / Repair / Restore
Mike,
I'm happy to give you a break. Like I wrote, nuff said. I can easily tolerate your style of posting. I also invite you to tolerate mine. See? We're friends.
howdy
martin
coming to PeachFest in August ?
Mike Smith Rhode Island : Design / Build / Repair / Restore
If I promise to post in the correct format, could someone tell me where I might find the information to determine the dewpoint in a wall structure.
The information here is great but at some point I have to come up with a plan to side this nightmare soon
I spent quite a while on the building sciences page but couldn't find a formula I could put data into to figure out a solution.
I'm happy to do the legwork if someone could point me in the right direction. If anyone has a preferred method for this situation I'm open to suggestions
Thanks to all for the responses so far.
i'll be back
but NRT Rob or some of the heating guys could probably do a better jobMike Smith Rhode Island : Design / Build / Repair / Restore
It's really pretty simple. You calculate the wall assembly R-value, including all layers and inside and outside air films. You then graph or calculate the delta-T through each element of the thermal envelope, both at the studs and in between. This will be proportional to the percentage of R-value that each element contributes to the overall R-value of the assembly.
If you draw the wall section, making each element as thick as its R-value (graphic at right), then make a temperature chart on the Y-axis and draw a straight line from inside temp to outside temp, you can determine the temperature at each point in the envelope.
Unless you want to look up the dewpoint for each particular temperature and relative humidity level, as a rule of thumb you can assume that any point at or below 45° will be a condensing surface at an indoor RH of 40%.
View Image
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 2/15/2008 7:37 pm ET by Riversong
Thanks River
Should I assume that the ideal would be to have the dewpoint fall somewhere in the XPS? If so, I would accomplish that by installing thicker insulation or is there a method to do that and stay with the one inch foam?
You can either add exterior R--value and move the dew point beyond any condensing surface, or simply make sure the wall assembly is sufficiently air-tight to prevent moisture from getting in, since almost all moisture in the thermal envelope comes from air transport and not diffusion.
If there isn't an air-tight inner wall, then making the outer wall airtight, but moisture permeable is the safest approach. Doing that with XPS is problematic, which is why I don't use foam on the outside (also siding nail penetrations reduces the overall R-value and can create condensation points). If you can find EPS foam, it at least is not a vapor barrier, and don't tape the housewrap joints so that any possible condensate can drain eventually.
That's about the best advice I can offer. Good luck.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
The dilemma in building (or renovating) for a cold climate is that we need to achieve two often contradictory goals:
keep all moisture out of the building envelope
allow moisture that does get in a way to get out
For new construction, I always follow the rule of thumb: make the outer skin at least 5 times as permeable as the inside skin.
On renovation, this is not always possible. So we have to make the best compromise by making the inside skin as vapor- and, especially, air-tight as possible, and allow the outer skin to be able to both breath and drain.
This is why it's critical for all outside drainage planes to be "shingled" downward, with every higher plane overlapping every lower plane:
narrow strips of paper better than wide strips of housewrap
building papers/wraps lapped over flashings
window/door gaskets lapped downward
impermeable sidings (vinyl) that incorporate drainage holes
Adding exterior rigid insulation can be a good strategy if the dew point can be moved out away from the wooden sheathing into the foam board. This might require 2" of foam, however, which makes nailing siding problematic unless vertical furring is installed to create both a nailing surface and a rain screen drainage plane. This also has the advantage of reducing the number of nail penetrations through the foam and placing the nails in the wood framing instead of through the wooden sheathing where they will create condensation points. But it makes a very thick outer skin which requires adapting window and door trim unless new units are installed.
Below is a graph from an excellent report on this subject available at http://www.eere.energy.gov/buildings/building_america/pdfs/db/35793.pdf
View Image
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 2/16/2008 1:28 pm ET by Riversong
Edited 2/16/2008 1:29 pm ET by Riversong
Hey Riversong. Great article. I bookmarked it and have read the first two pages and already feel that my understanding of vapour movement has increased.
Also ( I just have to kick this in :) there are some very well crafted paragraphs in it.
One question on the illustration. If different components in a wall section have different r-values would your line travel straight from od temp to id temp or would the different sections be plotted according to their individual characteristics. I'm currently reading and trying to digest the info from the last site you refered me to so if this subject is covered there please disregard this post. I appreciate your time and the knowledge you are so liberal with. I think with all the garbage on the net this is one of it's most redeeming qualities. Thanks again
One question on the illustration. If different components in a wall section have different r-values would your line travel straight from od temp to id temp or would the different sections be plotted according to their individual characteristics.
You replied to 100904.33, but it sounds like you're referring to the two cross-sections in 100904.25.
The section on the left is the actual to-scale cross-section of the wall and, as you'll notice, the temperature line drops through each element the same proportion of the overall delta-T as that element contributes to the overall R-value of the wall assembly.
The section on the right shows each wall element scaled to its relative R-value. This allows a straight line temperature graph to descend from T-in to T-out.
View Image
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 2/18/2008 9:36 pm ET by Riversong
Robert, do you have a preferred reference book for the information in your graphs, and in the thread about foundation insulation?
I don't know of any one reference book that covers all this well. Some of it is in The Visual Handbook of Building and Remodeling - Professional Edition, by Charlie Wing who was my original source for some of this when I studied with him in 1982. It's a great overall reference manual.
But some of my numbers are cranked out from the many dozens of spreadsheets I've created to do all my structural and thermal engineering. I just added a spreadsheet page to my above post to show where those numbers came from.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Hi Robert, At the risk of alarming any P.E.T.A. members, I would like to beat a dead horse again. I've been doing some research on all the information brought out in the last discussion about water vapor, dewpoints yada yada yada. I would like to ask your opinion on a product.
Benjamin Obdyke has a product called home slicker which is a material somewhat similar in texture to bubble wrap. It's purpose is to provide ventilation/drainage behind a variety of exterior finishes.
In speaking with the engineer from B.O ;) his opinion was that this product would resolve the issues with condensation forming by allowing any water deposited to drain through the integral channels. He also stated that having tyvek against the sheathing wasn't an issue because he felt the water vapor migrating from interior to exterior during winter months would pass through the tyvek and then condense on the outer face of the Tyvek.
Based on the info you provided and what I've found on the building sciences website, that doesn't seem right. If the temperature of the sheathing is at or below the dewpoint for a given set of conditions, the vapor will condense at wherever that dewpoint falls. Is this correct?
So in your opinion, if I use homeslicker would it be best to use tar paper under it rather that Tyvek due to the fact that it's hygrscopic and would tend to wick the water away from the sheathing should any condensation form? Or would it be best to just use the homeslicker under the foam and Tyvek on top of the foam? I don't mean to keep bothering you with this subject but I don't want to create a problem and spend $10,000 to do it. I appreciate any additional info you might want to share or opinions you might have. It seems every manufacturer I talk to has a different take on this issue, with each method seemingly condemning anothers approach. I find in the field hands on experience is sometimes the best litmus test. Thanks again.
Thanks for posting some of the most useful information that has been presented here in a while. I was going to drag out Rose's book and am glad that I didn't have to. By the way, this topic (in laymen's terms) would make an excellent article in FHB. You should consider submitting a proposal.
Another point to consider is that, as water vapor migrates outward through a building envelope, there are two mechanisms to create liquid moisture and moisture problems.
The first is when water vapor, diffusing through permeable elements, reaches an impermeable element that is below the dew point temperature. It is this mechanism which will cause condensation and wetting on the inside surface of sheathing or siding after passing through the wall and the housewrap. Interestingly, exterior grade plywood sheathing becomes more permeable to vapor diffusion once it gets wet, so initial wetting might allow the moisture to permeate outward harmlessly. If the siding is back-primed and there is an escape path for the water, this is not necessarily a problem.
The second is when water vapor, diffusing through permeable elements, reaches an air pocket that is below the dew point temperature. The water vapor will saturate the air in those pockets, condense on cold surfaces, and by doing so will dehydrate the air causing an increased vapor pressure differential which will draw more vapor outward. It is this mechanism which will cause condensation and wetting on the outside of sheathing before it reaches the housewrap. Plastic housewraps (Tyvek, Typar) are highly permeable to water vapor but impermeable to liquid water, so the moisture now is trapped between sheathing and housewrap, and often has no drainage plane because of taping of housewrap laps (even without tape, 9' "shingles" of housewrap don't allow easy drainage). So sheathing gets increasingly wet over time and problems may develop.
It is for this reason, among others, that building scientists are recommending bulding (red rosin) paper or 15# felt for exterior drainage planes instead of plastic housewraps. Rosin paper and felt are both vapor permeable and hygroscopic, so any condensing moisture can wick through them and be released to the outside.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Mike,
A celebration of peaches? Pie-baking contest? Harvesting from step-ladders? When I was younger, I worked as an apple-picker at an orchard in Vermont. I found it hard to keep up with the Jamaican crew I was working with, though.
it is just coinky-dink... there happen to be peaches there
Doud owns an orchard that raises peaches
hence " PeachFest" .... but it is really just an excuse to get together for a long weekend
in the tradition of :
Petefest (2000)... pete in Cleveland
Caperfest ( 2001 ) adrian in Cape Breton , NS
Texfest (2002).. james in Beaumont
ReckoFest (2003 ) .. doug in Massachusetts
Rhodefest (2004 ) .... mike in RI
Riverfest (2005 ) ... calvin in Ohio
TipiFest (2006 ) andy in Long Island, NY
Northfest (2007 ) ...dinosaur in Mt. Tremblant
so , stand up, hook up , shuffle to the door, and leap to your fateMike Smith Rhode Island : Design / Build / Repair / Restore
Sorry Mike but I agree with Martin that your posting style is much more uncomfortable to read - and such a waste of virtual space.
For a guy who demands tolerance from others, you can be pretty intolerant of different styles yourself.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
so bite me...
also... BTW... excellent graphs... very well done
Mike Smith Rhode Island : Design / Build / Repair / Restore
Edited 2/15/2008 9:49 pm ET by MikeSmith
The problem with only adding one inch of XPS is that under the right (or wrong) conditions, the dewpoint may be inboard of the foam which will lead to condensation of any vapor moving through the wall. Riversong seems to have some numbers for your consideration. Telling us your climate would be helpful.
Sorry about not providing more detail. I'm located on the coast of CT, about 2 miles inland from Long Island Sound near New Haven. The design temp for heating systems(I'm an HVAC tech) is 7 degrees in the winter months, but temperatures average 20 to 30 degrees for most of the winter lately. Thank you,global warming! Summer temps range from 70 to near 100, often with very high humidity. Hope this helps you help me. Thanks again
What is you climate?
What about using polyiso for the insulation. That is close to r-7 and will help the insultion.
And there are people that claim vinyl siding is nothing more than a rain screen.
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.