Metal Roof

Tommy and Bryce braved the heat recently to put on our galvalume metal roof. We only get to do this a few times a year, so it’s always satisfying to be up in the air, above the trees while bending and crimping metal.

We used the 26 gauge Advantage Lok roofing pan by Union Corrugating, which we get from Better Living. This mimics the look of a true standing seam, but it actually snaps and locks on the previous piece rather than getting field hemmed together. I would love to be putting on a true standing seam, but I have yet to find anybody that will sell me the pans. (Most roofing companies in town make their own pans and are generally interested only in making pans for jobs that they are going to install). Still, the Advantage Lok pans meet Miami Dade County’s rigid code for uplift in a hurricane zone, and we still get the fun of field hemming the eaves and rake of all pans.

I get all of my eave, rake drip edge, two-part non-exposed fastener ridge vent, and metal plumbing vent boots bent at Martin Roofing in town. I could get a lot of this from Union Corrugating, but since the trim detail is a bit more specific and complicated, I prefer to get it local in case I run short or have an issue. Plus, it’s a lot of fun to go into Martin Roofing’s shop and work with Neil on figuring everything out.

The big change for us on this roof is that we are actually not doing a conditioned attic like we have usually been doing, but are going the route of the more traditional vented attic (with soffit and ridge vents). We started going with the conditioned attic space and spraying the underside of the roof deck with open cell foam as we were running duct work up in that space and it’s obviously not efficient to run cool air conditioned air in a hot attic. For this house, we went with the traditional vented attic for two reasons:

1) We have no HVAC in the attic

2) Going with a 6/12 gable roof is a lot more roof area than the simple 3/12 shed roofs that we have doing, so it would take a lot more insulation on the underside of the sheathing. Plus, our Passive House modeling calls for R60 insulation in the ceiling, which is just prohibitively expensive for us in spray foam. But, achieving this with blown cellulose (recycled newspaper) is very affordable. Plus, since we already ran a plywood taped air barrier on the 2nd floor ceiling, we don’t need the air sealing qualities that spray foam would provide.

We also made sure to put all of our plumbing vents on the north side of the gable roof as Joey has been diligently investigating the possibility of a solar thermal hot-water system and/or a grid tied photo-voltaic system. Stay tuned…

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Exterior Doors…

Tom has been busy this last day or so both manhandling and finessing our extra deep exterior doors into place. While we went with the Serious 525 fiberglass series for the windows, we just couldn’t justify the extra cost for the Serious doors. Plus, all Serious is doing is buying prehung doors by Thermatru and slipping their own glass into them, so it’s still a conventional frame.

Instead, we opted to buy Thermatru Smooth-Star fiberglass doors with just double pane low-e glass in them. To meet the Passive House Standards with the higher U-value door glass, our modeling called for increasing our exterior wall insulation from ten to eleven inches. Just that extra inch of insulation is still a few thousand dollars cheaper than the cost of the triple-pane Serious glass in a standard Thermatru door.

A few wrinkles: We were able to get Thermatru to make a 12″ thick jamb, such that our doors hinge on the interior side of our double stud and are able to swing freely. However, the deepest sill we could get was only 8″ deep. So, if you look at the photos, you can see the jambs of the doors stick past the actual sill by a couple inches.

To solve this flashing issue, we had Martin roofing solder up some copper door pans for our doors to sit in. It is probably overkill, but we also ran rubber and caulk below our copper door pan as well. Also, before seating the door in the pan, we adhered a thick self stick rubber membrane to the bottom of the aluminum sill such that it wouldn’t be in contact with the copper, which could potentially react and corrode the aluminum.

As far as aesthetics, Joey went with a 3/4 lite for our two front doors to try and have a little bit of a unique look.

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Serious Windows

We have received our triple pane windows from Serious and have been busy working our way around the house. Today was spent installing the ten 5′ x 5′ double casements on the south side. More details next week. Feels great to be almost sealed up.

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Double Stud walls

Now that we are under roof, we’ve been concentrating on our interior framing.  First up was building the interior half of the double stud wall around the outside of the house.  It moved pretty fast except for continually having to shuffle things around to have room to build the walls.

Originally, our Passive House calculations called for a 3″ insulation gap between the two walls; however, that was with the triple pane Serious 525 doors.  Unfortunately, we found the doors to be not financially viable, so are instead using double pane Therma-Tru doors with triple point locking on all doors (more on this later).  To compensate for the slight loss in performance, we had to bump our separation to 4″, making the walls 11″ thick now.

As far as building them, it’s just a matter of copying the layout for the exterior wall.  We were able to add a little bit of value framing by not having to worry about exterior sheathing having to break every four feet and left out studs whenever a window was within two feet of that four foot layout.

These are definitely the straightest walls we’ve ever had as string-lining exterior walls still has a small amount of imprecision. In this case, we were able to chalk a straight line on the underside of the trusses all the way down and went ahead and attached the cap plate to this prior to lifting the wall up.

We can’t wait to get the windows installed and then jamb them out to really get a sense of the depth of the walls.

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Attic air sealing detail

We are trying a new attic insulation and air sealing detail on this house. We have been a big believer in conditioning the attic space in all of our houses and have been spraying open cell foam on the underside of the roof sheathing down to the top plate. Typically, we have been running the duct work for the 2nd floor in this attic space, so it makes sense that it is terribly inefficient to run duct work that is delivering cool air in a hot attic space. Also, because we mostly use low slope shed roofs, the volume of the attic is not generally that much of a space to condition.

For the Passive House standard, we need to achieve a ceiling R-value of 60. To do this in foam is just too expensive for us (more surface to cover with a gable vs shed roof), so we find ourselves returning to dry blown cellulose, which you see in most houses. Traditionally, the big downside for cellulose is that it won’t prevent air infiltration. The system of just blowing the cellulose over the ceiling drywall leaves potential areas of air leakage around lights, through drywall cracks and around the inside edge of the top plate. This was not going to work for us.

To get a great air barrier, we actually nailed up 1/2″ plywood to the underside of the trusses. Before even setting the trusses, we made sure to put down a small 6″ ripper of plywood on top of the cap plate of the wall and taped that outside corner of the plywood to the exterior sheathing really well. Once the trusses were set, we continued this plane of plywood all the way across the ceiling and taped all the seams.  We made sure this ripper of plywood projected past the interior side of the wall to have enough room to tape the seam.

We did have to notch into the plywood to attach the hurricane clips. We did our best to tape those notches, but I think I’m going to have to use a little foam there to seal the deal.

We are going with all sconces for lighting and will also put the smoke detectors on the wall, so we don’t have to worry about any penetrations of the plywood. If we were to have ceiling lighting, we would have to fir down a chase on the underside of the plywood. John Semmelhack had an interesting idea if we had to go this route of actually building a mini floor system on top of the wall plates of 2x4s or 2x6s and plywood. This would be installed before setting trusses too and the tape would have to be installed on the sky side of the plywood instead of the underside. Besides giving a chase in the conditioned space to run recessed lighting or duct work, this would create a platform to set trusses on, which ups the safety and ease of installation for truss setting.

As far as costs, I really don’t think there is much of a cost increase from this method. Because cellulose is so much cheaper than foam, the insulation cost savings makes up for the cost of the material and labor of installing the plywood. It’s a slightly different story if we were to build a false floor system though, as the labor and material costs from that would be moderately significant.

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Serious Windows

So, again, for this next house, we are going for Passive House Certification, which is still fairly new to the States, but has been around Germany for quite awhile.  A quick refresher: Rather than just being a points based system like LEED or Earthcraft, Passive House sets rigid standards that must be met both by computer modeling of the building and verification and testing in the field. Rather than relying on fancy and expensive systems like geothermal heating or solar hot water, the focus is on super insulation, airtightness and controlled fresh air.  One of the ultimate goals of Passive House is to have a home that uses 10% of the heating and cooling load of a normal house.

One of the biggest factors in achieving this is the windows.  We ended up going with the 525 series by Serious Windows for a number of reasons.  First, and most important, we are able to meet the Passive House standards with these windows.  It’s a combination of the window being triple pane and the thoughtful construction of the fiberglass frame.  When you look at the specifications of most new windows, they show the U-value of the window (which is the inverse of the R-value and refers to the thermal quality of the window).  However, this U-value is sometimes just the glass, and doesn’t take into account the whole window, including the frame.  When you get windows with really high performing glass, the frame of the window becomes the weak point in the window. The Serious 525 series has a whole window U-value of .22 (4.5 R-value) for the casements with high solar heat gain coefficients that we are using.

Serious has even higher performing lines of triple pane windows, but we are working with a modest budget.  Ultimately, it came down to price as other European and Canadian brands were just not affordable to us.  Even with Serious, we are paying about 65% more than what we have been spending on the Pella Proline series, which we have been really happy with in all our other houses. Honestly, if this was one of our spec houses, I don’t think I could afford to pull the trigger on these windows at this point because of the price as I unfortunately don’t think the market values all these energy savings though I’m hoping that will change.

The price of these windows was really the biggest moment of pause for us on whether to continue with Passiv House.  We calculate the payback as taking at least 20 to 25 years versus going with the Pella Proline, which is a long time.  But, there a few other advantages and cost savings because of these windows.  One benefit is the potential for condensation on the insides of the windows from relative humidity should be cut dramatically down. Another is the increased comfort level of hanging out close to the window and not feeling that temperature difference that you might feel with a double pane in the middle of winter. Coupled with the tightness of the house, the super insulation, and the ERV system, we are able to drastically reduce our heating and cooling load and go with a much more inexpensive hvac system.

Another cool aspect of the Passive House standard is that through modeling you actually spec different glass for different windows based on location.  Initially, this sounded really forward thinking and intuitively made sense as you would want a higher solar heat gain window on the south side, but not the west, to actually have the sun warm the house in the winter, but not overheat it in the summer.

Interestingly, the orientation and specs of our house dictated that we need high solar heat gain windows on all of our windows (SHGC=.40), which turned out to be a blessing.  For, you get much better visible transmittance with the high solar heat gain windows.  The 7, 9 and 11 series Serious windows can have either a blue or greenish tint to the glass and is noticeably darker.  This really catches your eye when you have two different types of glass in the same room, which we would have had because of the open floor plan.

Overall, I think we have always tried to strike that balance on our houses of having strong passsive solar orientation while still taking into account privacy, views and aesthetics. For us, it’s usually a bit of compromise when building in town on gridded infill lots.   My big take away from this experience thus far is starting to take into account the glass to frame ratio of the windows we use.  For example, it’s much more efficient to have one giant window rather than two smaller windows of the same area as the glass to frame ratio is usually better with one big window.  Anyway, yet another consideration to throw into the mix when designing future houses.

I’ll probably ramble on a little bit more about the Serious windows when we get them from Colorado in another month or so.

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Framing Begins!

Enough with the rain already.  We finally caught a break from mother nature today and were able to get rolling.  We knocked out the basement walls and set most of the web floor trusses for the 1st floor.  The biggest difficulty was navigating all those metal mending plates on the trusses.  Today was first for me: I had two pairs of shorts get completely torn to shreds.

Again for our Passive House certification we are actually building double stud walls with a three inch insulation gap in between.  For now, we’re holding off on one set of the double stud walls and are concentrating on getting under roof.  We are also forgoing our normal 1″ of rigid foam board that we have been wrapping our house with as we no longer have to worry about thermal bridging from a single stud wall.  To ensure complete air tightness, we are using heavy duty window wrap on all the plywood sheathing seams, which will then be convered in tyvek.

My only question is what’s on Tommy’s mind and why is he holding that saw?

 

 

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Beyond What is Easy


What’s easy is caulking every seam in your home and wrapping the exterior in foam to make it airtight.
What’s easy is investing in high performance energy recovery ventilators to heat your home like never before (the 1970s).
Beyond what’s easy is modeling all the components of a home in a computer simulation so that you can know exactly how it will perform in any situation.
Latitude 38. Beyond what’s easy.
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Latitude 38 has teamed up with John Semmelhack, owner of Think Little, to certify our most recent homes through the EarthCraft program. Getting our houses EarthCraft certified has provided Latitude 38 homeowners with the peace of mind that comes with knowing that an independent party has verified that they live in healthy, energy-efficient homes. But in the end we’ve still been left guessing about how certain design decisions will impact the energy performance of our homes.
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No longer. Latitude has joined forces with John again to work on certifying our next project on 6th street to the Passive House standard. Meeting the Passive House standard, arguably the most stringent standard for home energy performance out there, requires careful planning and extensive computer modeling. I sat in on a meeting with John recently and watched as he tweaked various components of the home in the Passive House Planning Package. We increased the thickness of the walls and the overall energy performance didn’t change nearly as much as I expected. We replaced our usual windows with triple plane windows and watched our performance figures drop substantially, but at an additional cost that would likely take 20-30 years to payback in energy savings (though, it should be noted that high performance windows come with other benefits like increased comfort and reduced condensation). After watching John alter several variables and seeing how they influence overall energy use, it is all too obvious that designing a house that functions optimally takes very careful planning.
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I’m proud to say that Latitude 38 won’t be shooting from the hip anymore, at least not when it comes to home energy performance. We owe it to our homeowners to build the best houses that we know how, and energy modeling will play an important role in living up to that obligation.

 

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