The frame of our sun porch is a combo of post and beam and pole building construction. The rafters are locally milled full dimension 2×6’s and all the posts, beams and stringer lumber are commercial pressure treated standard dimension lumber (nominally 2×8’s, 4×6’s and 6×6’s).
We have three panels up on the sun porch roof so far. Picture me wiggling in delight. I REALLY like this method of building a sun porch.
I purchased sun porch plans from CountryPlans.com. If you’re not a “leaps of logic, connect the dots” person, I recommend you purchase the plans. They’re relatively inexpensive and give a good run-down on how to assemble a sun porch. The construction they use is a little bit different and mounting the panels is a bit different, but sealing the roof using butyl rubber tape should be the same.
CountryPlans sun porch plans say to use glazing tape under the panels. I’m using putty mastic. Yeah, yeah, ever the rebel. As this bit of construction is a test for later construction, I’m trying two different types of mastic. Because I already have it on hand and it’s surplus, I’m using the putty mastic we got with the metal roofing for the barn/shop. It’s very like the putty that comes in a can which is used to set glass panes into wood frames (old type stuff) only doesn’t seem to harden much with age. The other is an all purpose acrylic silicone (includes window setting as one of the uses) compound in a tube I picked up at Ace. One tube does 1.5 panel mountings so mastic for the whole 6 panels would have cost just around $30.
I’m viewing the mastic as a pliable weight distribution base for setting the windows, not something for seal joints against moisture penetration. There is no such thing as moisture sealing something when the mounting is against raw wood.
Ideally I want the edges of the panel to have consistent pressure around the entire panel to ensure the panel doesn’t end up stressed to fracture. Bear this in mind if you decide to build a sun porch. You want a consistently even surface on which to mount the panels so the stringer installation is important. You want the support members (rafters) to be strong enough to support whatever weather (snow load) you get. The panels are relatively flexible but over-bending will result in broken glass. That’s one of the reasons I’m not using the 4′ wide panels as roofing panels – lack of support.
Ideally, pressure treated 4×6 beams would be the ideal rafter for this sun porch, but I already had rough cut 2×6 so that’s what I used. If we get a significant snow I’ll keep an eye on the roof to see how it holds up. I expect it to be okay but will have a temporary t-bar support planned should it look as if our infrequent “big snow (~30-36”) suggests additional support is needed.
Because we have amassed a lot of used windows, we have sliding glass door units in varying dimensions. I think we even have 2 sliders with ~4′ wide panels which we’ve earmarked for sun porch walls. If you’re wondering how I ended up with so many sliding glass door panels, here’s the deal. Home owners are swapping out aluminum framed sliders and sliders whose panels have developed leaks for more energy efficient vinyl and/or wood framed units. The old aluminum framed and leaking sliders are out there begging to be collected up and recycled/reused. Strip the aluminum frame, remove the roller and handle hardware, recycle the aluminum and use the double paned glass panels to build a rocking sun porch or green house for just the cost of the lumber, fasteners, mastic and butyl rubber tape.
Some of the panels we got are no longer sealed. For this particular application I don’t care if the panels have or can develop moisture inside. This sun porch is a test of the building method and serves as a temperature moderator for the sliding glass door into our living room, not as the roof of a place I plan to serve lunch with linen napkins. When we start building on the hill, sealed panels will matter. At that point, I will rebuild broken sealed panels and/or purchase new. Don’t hold your breath waiting for me to ever serve lunch with linen napkins. I am SO not Martha Stewart.
Because we are using sliding glass door panels in disparate sizes, the “as we go” construction works really well. Each bay is completed before the rafter of the next bay is put in place. This lets us use panels of different widths, lengths and thicknesses without affecting the integrity of the roof.
I started building at the outside edge planning to fill in between the adjacent building and the last bay of glass panels with conventional construction. It is pure serendipity that the panel width combos are exactly the right width to connect the outside wall of the adjacent building without any infill.
We put the first rafter up (left most rafter in the first picture), measured the width of the panels destined to go in that frame bay and cut the stringers (2×8 pressure treated) 1″ shorter than that measure. We butt screwed the bottom panel support stringer (see detail image)
The bottom stringer was beveled and channeled to act as a stopper for the bottom edge of the lower panel. In the stopper detail image you can see the bevel. The bluish bit is the window, the brown/gold wood is the stopper sitting on top the beam the stopper and rafter sit on. The faded wood grain is the rafter and the little bit of gray under the bottom edge of the glass panel is the putty mastic. There is an error in the image. <wince> I’d already trashed the working file when I caught the error. In actuality, the top surface of the rafter is even with the beveled panel seat on the stopper. The mastic continues all the way around under the panel including on top the rafter.
The stopper is butt screwed to the rafter. The panel is supported all the way around the outside edge of the panel. The panel sides sit on the rafter, the top and bottom sit on stringers. The entire outside edge is sitting on a bead of putty mastic.
The first bay of panels are 5/8″ thick and 32″ wide by 74″ long. The second bay has 5/8″x34″x76″ panels. The third and final bay will have 34″x76″ panels but I’m not sure what the thickens will be . . . maybe 3/4″. I have one slider side stripped and it’s 3/4″ thick. If I find a match for it, that’s what I’ll use.
Every time you build something, you learn what works and what you’d change if you were to do it again. I’m really glad I have a chance to test the construction method before using it for the sun porch for our house on the hill. There are a few key things I would do differently. When we build on the hill, I will notch the rafters where they meet the supporting beams at the peak and base of the rafter. I don’t see this as being a strength issue, I see this being a practicality issue. Notching the rafters facilitates attaching the rafter to the supporting beam. It also makes insulating the final result easier.
Additionally, I will install the bottom stopper stringer to the inside edge of the beam instead of flushing it to the outside edge. That will allow me to insulate the outside of the stopper and will allow any moisture running down the bottom side of the panel to drip off the beam face to the floor instead of pooling on top the beam. The devil is in the details. The beam is pressure treated, but it makes more sense to facilitate the running away of any moisture instead of providing a surface on which it can collect. This was a real duh moment, but you can only perfect a design by doing the design.
And one final piece of advice. If you have to use panels in a single bay that vary in thickness, put the thicker panel at the top. This will prevent water pooling where the thicker and thinner panels meet.