Timber Frame Hybrid Home - Owner Builder

[EddieWalker]

I don't know enough about spray foam insulation to disagree with you, but I would be very very sure that you are right before committing to so little ceiling insulation. From what I understand, the ceiling accounts for the vast majority of heating loss and where you see the biggest return on energy savings. If it where me, I would look into increasing the thickness of the roof and add fiberglass to the spray foam to get at least R60 by lowering the ceiling height.

Eddie

 

[jk96]

Fireplace off set elbows? Metal flue double wall right? Is there any way to do that without offsets because a straight run all the way is always better. Is this going to be a regular fireplace or an insert(sorry, I looked but could not find a reference to it?

Merry Christmas!

Correct - Stainless double wall flue, 16" inside diameter. There is no way to get around using the offsets. We have a ridge beam center of the chase to get around. We will use two 15 degree offsets for this. The flue mfg allows up to 4 offsets. The fireplace is a wood burning insert that draws combustion air from the outside of the house.

I don't know enough about spray foam insulation to disagree with you, but I would be very very sure that you are right before committing to so little ceiling insulation. From what I understand, the ceiling accounts for the vast majority of heating loss and where you see the biggest return on energy savings. If it where me, I would look into increasing the thickness of the roof and add fiberglass to the spray foam to get at least R60 by lowering the ceiling height.

Eddie

I appreciate the advise Eddie however I just don't believe the cost vs return is there. Even talking to our installer he recommended using 4" in the ceiling as opposed to paying for the additional 1-1/2". One thing to remember about the spray foam is the elimination of air movement. If installed correctly you are creating an airtight envelope that just is not possible with fiberglass insulation. This is one of the biggest advantages of spray foam. Closed cell also acts as a vapor barrier. Here's a chart showing the heat flow resistance as the thickness and R-value of spray foam increases. There is just not much gain past our current plan of using 5-1/2" of foam.



Edit: Eddie - Please don't think I'm downplaying your advise. It is greatly appreciated. I am by no means an expert on insulation, I'm just going by what I've researched and my discussions with other builders. I'm always open to suggestions provided I can show a return on investment. I'd love to hear others advise, especially those with some expertise on spray foam.

 

[MotorSeven]

I think R60 in Missouri is a bit of an overkill, not so much in Minnesota though. My roof R-value is around a 20 R-value and I have vaulted open beam ceilings up to a little over 20'. I am heating the whole house from the basement with a wood stove(which is not the optimum place to heat from). It was 17 degrees here this AM, with basement temps at 80, main floor at 68 degrees. At 67 or lower we are a bit uncomfortable, but so far heating solely with wood has worked out fine.

 

[dave1949]

I don't know how much difference it makes, but I noticed the foam chart is based on a 40* temperature difference. That is on the low side for heating in northern climates. For example, it's 4*F here at the moment. 4+40 = not warm enough :laughing:

I'm glad the OP shared the chart as I wouldn't have guessed at those percentages per inch of foam. My personal experience with a cathedral ceiling was not all that good. But, it was fiberglas insulation, not foam. Lots of heat goes up to those ceilings. Mine was 23' high, and not nearly as many sq ft as this one.

 

[jk96]

I don't know how much difference it makes, but I noticed the foam chart is based on a 40* temperature difference. That is on the low side for heating in northern climates. For example, it's 4*F here at the moment. 4+40 = not warm enough :laughing:

I'm glad the OP shared the chart as I wouldn't have guessed at those percentages per inch of foam. My personal experience with a cathedral ceiling was not all that good. But, it was fiberglas insulation, not foam. Lots of heat goes up to those ceilings. Mine was 23' high, and not nearly as many sq ft as this one.

January is our coldest month here. In looking at the the average temp for our location we have an average high of 38 and average low of 18 for the month of Jan. The 40 degree difference is a little low but not too far off for our location.

Our cathedral ceiling in the timber frame portion of the house is about 1000 sq/ft so there is going to be a significant amount of heat rise. This is where I'm hoping the tightness of our insulation envelope is going to pay off with foam. We have a couple of large fans going up there as well to help keep the air moving.

 

[EddieWalker]

I'm sure you will be fine with five inches of foam. I only suggest more because this is the only time it will be easy and affordable to max out how much insulation you have. I was just watching a Mike Holmes show on DIY Network and hey he was working on a house with 2x4 rafters. They added two inches to the rafters and spray foamed them to get five inches of foam. This was somewhere in Canada, and he felt that was plenty, so I'm not saying you are wrong, or it will be bad at all.

Eddie

 

[BitChin1]

Wow - just found this thread today (doing some research for a barn I am getting ready to construct) but while reading the thread I noticed that I had actually seen your frame before (in the shop getting cut by the TF'er that did my house last year):drink: quite a small world this is.

I see you are working through many of the questions I had - in the end I went with mostly SIP (much less complicated roof line) but also used spray foam in basement walkout, small bump-out room and bonus room over the garage. In my case the cost was a bit more for SIP but went up very much more quickly.
In the areas we spray foamed I had had good experience, but suggest you pay attention to detail (are you getting blower door test?) - the SIPs were stupid simple, the spray not so much. That said be sure you go over the details with Spray contractor before he starts and then look over the work. warm surface for foam to adhere to is critical - also look for areas of thermal bridging. I have run into as in an area framed with 2x6 that I can feel the difference between wall portion with foam and the section that is solid wood - we also had a couple places after the contractor sprayed where the detailing did not block all air passage - we found these once it got cold - luckily they were easily accessible from exterior and since fixed.

As for function - I am pleased; our results so far (occupied house Feb 2013) are very good - house is total of ~ 4700sqft (basement, main, loft, and bonus) - total elec with 3 ton geo for main area and basement with a 1T mini-split in the loft and in the bonus room over garage - we have large area of windows facing south so get very good heat gain (although last week there was not much sun) - have not had any trouble cooling or heating with this set up. My HVAC cont wanted to put in a 6T geo, but we settled on the 3T as this was the smallest he could install (we have open loop well -> well) (we are located a bit south of you in Wichita area but similar temps/solar exposure).

love you photo's - will keep up with this thread and interested in watching your progress -

 

[Larro Darro]

Welcome to the forum BitChin1. We all wait around with baited breath for jk96 to update this thread.

Larro

 

[IXLR8]

One thing to keep in mind is the R value of the wood, which if I remember correctly is 1. So you may have an R value in the foam of 38 in 2x6 construction, but for the 1.75" width of each 2x6 you only have an R value of 5.5 which can be significant across a roof/wall. Maybe not so important in Missouri, but is meaningful in Minnesota or Maine. Putting a 1" foam board over the inside would double the R value in the area of the 2x6's.

 

[BitChin1]

One detail you will need to cover is areas that have 2 or more 2x's together - the spray foam won't get between these boards but air will - get a good caulk that will stay flexible and stretch - fill all of these including near timbers - actually these were some of the most difficult I found as the spray foam could not get behind them very well and your timbers will shrink (hence needing the stretchable caulking that stays flexible forever)
Also pay attention to the paper wrap - tape all tears/joints/transitions
Key to HVAC/insulation performance is air-sealing (that or $'s paid to utility company) - you don't want to give the money saved now to monthly bills increase later

As for your "extra 2T" heat-pump be sure the contractor is increasing unit and field loop (or explain to you why not) - now in reality your home should never need anything close to 8T (unless you don't get the air sealing right?), so your real interest is in low speed operation and how efficient the unit you are installing will be when minimal load is called for