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A hybrid of the traditional sun porch and the solar collector, a sun space combines the best features of both. As a porch, it provides new living space; as a collector, it works like a greenhouse, trapping solar heat within its transparent walls and roof and storing it in the thermal mass of its insulated masonry floor. The temperature inside a sun space can reach 85° F. or more on a sunny winter day—even when the temperature out of doors is well be low the freezing mark. The warmed air, pulled into the house by a through-the- wall fan (-- 61), can significantly re duce heating bills. A sun space is most effective in areas with mild climates—those rated below 3,500 heating-degree days ( 8-9)— but the structure may be modified to suit the harsher weather conditions of other regions. In climates with 3,500 to 5,500 heating-degree days, only part of the roof should be glazed; the upper half should be insulated to help retain as much of the heat of the sun-warmed air as possible. In even colder climates, where more heat would be lost through large areas of glazing than gained through sunlight, the sun space will collect and retain heat most effectively if only the south wall of the structure is glazed. A sun space must be carefully oriented to take full advantage of the sun’s warmth. It should be attached, if possible, to the house wall that faces most directly toward true south ( 8-9). The orientation may range up to 45° east or west of south, but a variation of less than 15° is ideal. To prevent prevailing winter winds from robbing a sun space of heat—and to ward off the hot afternoon sun during the summer—the west side wall is frequently closed in, as shown in the example opposite. If the south wall faces more than 15° east of true south, the opposite arrangement is sometimes advantageous: The east wall is insulated and the west wall is glazed. Any unglazed section of a sun space is constructed like a conventional exterior wall, with 2-by-4 studs sheathed in ply wood and covered with siding that matches the house. The comparatively weaker glazed walls are mounted on a sturdy post-and-beam frame of 4-by-4 cedar, redwood or pressure-treated lumber. All of the wooden framing pieces should be treated generously with a wood-preservative stain if you want a natural finish; if the structure is to be painted, use exterior trim paint. A sun space must be shallow so that sunlight can penetrate its full depth. The side walls should be no more than half as long as the south wall, and the dimensions are further governed by the layout of the walls and doors. The most economical and readily available glazing material for the walls is the type of replacement panel sold for sliding glass doors. These panels come in standard sizes; the design shown here uses panels of 46 by 76 inches. The length of the south wall is determined by the number of panels that are used. The length of the side walls, one of which contains a sliding glass door to provide access to the outside, is based on the width of the particular door unit that you have chosen. Because doorframe sizes vary slightly, be sure to measure the door you will actually use before laying out the sun space. The size and slope of the roof are determined largely by the position of the existing second-story windows. The roof must meet the house wall below these windows, preferably at an angle between 30° and 40°. The steeper the pitch, the more sunlight the roof will capture in winter when the sun’s arc is low in the sky. The roof is the most vulnerable part of a sun space. It must admit sunlight, yet resist hailstorms and melting snow with out breaking or leaking. Double-wall, 5/8 inch-thick sheets of acrylic, available from suppliers of energy-conservation products or from greenhouse companies, offer virtually the same light transmission and insulating qualities as double-glazed glass panels, yet are far tougher. They are also lighter, making them safer and easier to install. The material comes in a standard 47.25” width to fit across rafters spaced 48 inches on center. It can be trimmed to the proper length with a circular saw. Because acrylic expands and contracts in response to temperature changes more than glass does, the panels are installed in a special aluminum frame (-- 74) fitted with silicone-coated gaskets that form a tight yet flexible seal against water leakage. To keep heat from escaping, a sun space must be airtight. As you build it, bevel the joints and plane the framing members so that they fit snugly. Stuff fiberglass insulation into all spaces behind trim boards or blocking. Use silicone caulk to seal joints, taking extra care where the sun-space frame meets the house wall and along the top edges of horizontal trim—areas that are especially vulnerable to leaks. The concrete-slab floor of a sun space is a crucial part of its design. To retain the warmth it absorbs from sunlight, the floor is insulated with 2-inch styrene foam boards laid around the foundation walls. For additional thermal mass, you can place containers of water in the sun space, making sure that they are positioned where direct sunlight will strike them; like the floor, the containers collect heat during the day and radiate it at night. Designers of solar heating systems generally recommend 3 to 5 gallons of water for every square foot of glazing on the south wall. To further increase the light-absorbing qualities of the sun space, the floor and rear wall should be painted a dark color, or the floor may be covered with dark flagstone, slate or quarry tile. During winter nights, a sun space will lose heat quickly through its extensive glazing. Insulated fabric shades or pop-in shutter panels wedged between the posts and rafters at night can be used to conserve some of this heat. Window shades can be used to block the sun during the summer, and summer shading of the roof is essential to prevent overheating. Nature’s shades are another alternative for warm months: Deciduous trees, a row of giant sunflowers or an overhanging trellis of vines will cool the sun space in summer, then die back in winter to allow sunlight through when it’s wanted. Local building codes vary: Your area may require different construction details from those shown here. Have your plans approved before starting. 64 Anatomy of a sun space. Attached to the southernmost wall of a house, the 4-by-4 post- and-beam framework of a sun space rests on a concrete-block foundation that supports the slab floor. The outside of the foundation is insulated with 2-inch-thick styrene foam boards to hold in heat absorbed by the slab. Facing the sunny south, the broad front wall of the sun space consists of 46-by-76-inch double-glazed sliding-door panels mounted between 4-by-4 posts spaced 48 inches on center. The east side wall is fitted with a sliding door. The west side wall is built like an ordinary wall, sheathed in plywood and insulated. The triangular space above the east wall is filled in with double-glazed acrylic panels. The roof is glazed with acrylic panels, mounted in aluminum frames set on 4-by-4 rafters. Two skylights in the roof open to al low excess heat to escape during warm months. If opening skylights are not used, the roof must be vented. A thermostatically controlled fan like the one --- 61, installed behind a vent in the house wall near the roof peak, pulls warm air into the house; the vent near the floor returns cooler house air to the sun space. Metal drums filled with water add thermal mass to that of the heat-gathering slab and double as a convenient base for a tabletop. Building the Foundation 1. Making square corners. Mark the house wall where the sun-space foundation will meet it. Nail 8-foot, 1-by-2 marker boards to the wall, with the boards extending 3½ feet inside the corner marks, their top edges level and 16 inches above the intended height of the slab. Make sure the two boards are level with each other. To establish right angles from the house wall, drive one nail into the top edge of each marker board at the corner mark and a second nail 3 feet in from the first. Have a helper hook the end of a tape measure to each nail and cross the two tapes so that the 4-foot mark on the corner-nail tape meets the 5-foot mark on the other tape. Drive a 2-by-2 stake into the ground at this point. Extend lines beyond the stakes, and drive two more stakes to mark the outer corners of the foundation. Drive a nail into the top of each corner stake. Check the foundation for squareness by measuring diagonally from the nails on the marker boards to those on the corner stakes --. If the diagonals are not equal, ad just the position of the corner stakes. 65 2. Setting up batter boards. To form right angles around the corner stakes, drive three 2-by-4 stakes into the ground about 5 feet away from each stake. Using a water level as a guide, mark the height of the marker boards on the 2-by-4s and nail 1-by-6 horizontal batter boards across them, setting the top edges even with the marks. To mark the side-wall locations on the batter boards, stretch a string from the corner nail (-- 65, Step 1) on each marker board to the batter board placed parallel to it, passing the string over the nail in the foundation corner stake --. Drive a nail in the top edge of the batter board where the string touches it. To mark the outside edge of the south foundation on the other batter boards, stretch a string parallel to the house wall over the nails in the foundation corner stakes. Drive nails where the string crosses the batter boards. Remove the right-angle stakes and corner stakes. 3. Marking the footing position. Drive three more nails into each of the four batter boards and the two marker boards, following the pattern and dimensions shown. Those spaced 7 inches apart represent the outside and inside edges of the foundation walls; those placed 4 inches on either side will serve as guidelines for digging a 16-inch-wide concrete footing that will support the foundation. Outline the inside and outside dimensions of the footing by stretching strings between the appropriate nails on the batter boards and marker boards. With a plumb bob and a squeeze bottle of lime or chalk, mark the string positions on the ground about every 2 feet and connect the marks, Remove the strings and dig a 16-inch- wide footing trench. Measuring from the top of the marker board, dig the trench to a depth that is below the frost line and is a multiple of 8 inches to allow for an 8-inch-deep footing and for the 8-inch concrete blocks that will be used to build the foundation. To dig to the bottom of a very deep footing, you may need to widen the trench around the outer perimeter. However, the trench for the footing itself must be 16 inches wide and 8 inches deep, with straight walls and a level bottom. 66 4. Leveling the footing trench. Drive 1-by-2 stakes along the sides of the trench, 3 feet apart in a staggered pattern. Measuring down from the marker board, mark the first stake at the depth for the top of the footing; transfer the mark to the other stakes, using a water level (Step 2). If the mark on any stake is less than 8 inches above the trench bottom, dig out the trench farther. Don’t fill in any depressions deeper than 8 inches. Drive a grade peg—a 16-inch length of ½-inch reinforcing bar—next to each stake and another directly across from it, 3 inches from the walls of the footing trench. Set the top of each peg level with the mark on the stake; remove the stakes. 5. Reinforcing the footing. Lay two lengths of rein forcing bar in the trench, one along each row of grade pegs. Prop them up with bricks, and wire them to the grade pegs. Where two lengths of reinforcing bar must be joined, overlap them 15 inches and wire them together. Pour concrete into the trench to the tops of the grade pegs. Spread it with a shovel or a rake, and smooth the top with a float. Cover it loosely with polyethylene sheets and let it cure for 24 hours. After removing the polyethylene, stretch strings between the nails on the marker boards and batter boards that mark the edges of the foundation wall. Use a plumb bob and lime (Step 3) to mark the string positions on the footing, and connect the marks by snapping a chalk line --. Remove the strings. 6. Building the foundation wall. Lay concrete blocks between the chalk lines on the footing, starting at the corners and ends to provide leads for the wall courses. Run a mason’s line between the leads to keep the courses straight. After laying a course of blocks, fill the cores with sand or concrete to add thermal mass to the wall. Brush off the block surfaces so that the mortar of the next course will ad here. If the wall will be more than three courses high, lay a strip of wire-mesh reinforcement into the mortar bed of every third course. For the top course, lay L-shaped shoe blocks (in set) to contain the edges of the slab floor. Use solid shoe blocks for the south wall and one side wall, and cored shoe blocks for the side wall that will contain the sliding door. The cores will later hold anchor bolts to secure the sill plate. Plug the gaps left by the corner shoe blocks, using scrap brick and mortar. 67 1. Pouring the slab. Backfill the trench inside the foundation walls, tamping the dirt level with the bottom of the shoe-block course. Spread 3 inches of gravel over the slab area --, and level it with a screed made from an 8-foot-long 2- by-4. Cover the gravel with a vapor barrier of 6-mil polyethylene, overlapping the sheets 12 inches at the edges. Run strips of 4-inch expansion-joint filler along the house foundation wall and the shoe blocks. Roll 6-inch wire-mesh reinforcement over the slab area, flatten out the mesh, then slip bricks under it every few feet to elevate it. Pour in concrete, leveling it with the tops of the shoe blocks and filling the shoe-block cores along the side wall. Screed the concrete. 2. Installing anchor bolts. At the wall that will support the sliding door, mark positions for anchor bolts in the wet concrete of the cored shoe blocks. Start 1 foot in from each corner, and space the bolts 3 to 4 feet apart. Make a jig for each bolt by drilling a hole through a scrap of 1-by-4. Insert the bolt through the hole, slip a washer onto the shank and screw on a nut flush with the top of the shank. Sink the bolt into the concrete until the 1-by-4 touches the surface. Leave the jig in place until the concrete sets. 3. Smoothing the slab. After the concrete in the slab has set for 30 minutes, use a wooden float and a metal trowel to smooth the surface. Sup porting yourself on knee boards—plywood rectangles with a 2-by-2 nailed to each end—repeatedly sweep the float over the concrete and follow with the trowel. Work on half of the slab at a time, moving from the middle of the house wall out to the slab edges. When the surface is smooth, spray it lightly with a hose and cover it with 6-mil polyethylene. Let the slab cure for three days. While the concrete cures, build a knee wall by laying one course of 4-inch-wide cored concrete blocks on the outside perimeter of the south foundation wall and the side wall that won’t contain the sliding door. Set an anchor bolt every 4 feet into concrete in a block core (Step 2); fill the remaining cores with sand. Pouring, Smoothing and Finishing the Slab 68 Insulating the foundation. Squeeze dabs of construction adhesive at 1-foot intervals in two rows on the back of 2-by-B-foot, 2-inch- thick, styrene foam insulation panels. Press the panels against the foundation wall, with the long bottom edge of each panel flush with the top of the footing. Trim the panels as necessary with a utility knife to cover the entire foundation and knee wall up to the top edge. Coat the surface of the insulation and the interior of the knee wall with a commercial surface-bonding cement. After the coating has cured—about 24 hours, depending on the manufacturer’s instructions for foam—back fill the dirt around the foundation up to grade level, and tamp it firmly. Putting Up the Wall Frames 1. Setting the sill plates. Using a circular saw, cut 2-by-8 sill plates. The south sill should ex tend 1½ inches beyond the foundation insulation at each end; the side sills should reach from the house to the inside edge of the south wall. For a waterproof drip edge, cut a 30-deg. bevel 2 inches wide down the top surface of each sill. Then cut a lengthwise kerf on the underside of the sill about an inch in from the edge. To position a sill, set it on top of the anchor bolts with its inside edge even with the inside edge of the blocks below it. Imprint the anchor- bolt locations by striking the sill over each bolt with a mallet, protecting the wood with a piece of scrap. Drill holes for the bolts at these marks, and counterbore ¾-inch-deep holes in the top of the sill to accommodate the anchor-bolt nuts. Set an 8-inch-wide strip of flashing across the top of the blocks, then unroll a strip of sill sealer—a thin strip of insulation—across it, pushing the bolts through it. Set the sill plate in place -- and tighten the nuts on the anchor bolts. 69 2 Erecting the corner posts. With the aid of a helper, plumb the two outside 4-by-4 corner posts and toenail them to the south sill. Nail temporary 2-by-4 braces to the posts and sills. Snap vertical chalk lines on the house wall to mark the positions of the inside corner posts. Allow an extra 1/2 inch of width for the corner post of the covered side wall to accommodate the sheathing of the new wall. Cut away the house siding between the lines with a circular saw. If there are studs in the wall at the post positions, fasten the posts to them with ½-by- 6-inch lag bolts. Otherwise, use toggle bolts to anchor them to the wall sheathing, or bolt the posts to nailing blocks installed between the studs. Attach corner posts to masonry walls as shown in Step 2. 3. Installing the headers. Install and brace the post nearest the middle of the south wall. Span the three south wall posts with two 4-by-4 header beams, notched 1¾ inches by 3½ inches at each end for lap joints. Fit the header sections together, and nail them to the posts and to each other at the notches --. Similarly notch one end of each side-wall header to fit the outside corners of the sun space. Square-cut the opposite ends, and toenail them to the posts at the house wall. Insert intermediate posts into the south wall every 48 inches on center, and toenail them to the sill and header. To frame the side wall that will be sheathed, toenail 2-by-4 studs every 16 inches to the sill plate and the header. 70 2x4 TEMPLATE Framing the Roof 1. Attaching the rafter plate. Cut a 2-by-6 rafter plate as long as the south wall of the sun space, or use two boards butted end to end. Mark the intended location of the roof peak on the house wall by measuring up from each side-wall header, then snapping a level chalk line across the wall. Find the studs in the wall by drilling a hole through the siding just below the chalk line and probing with a wire. While a helper holds its top edge along the chalk line, tack the rafter plate temporarily to the wall. Shim behind the plate as necessary to plumb the face. Drill a ¾-inch pilot hole through the middle of the rafter plate into each stud, and insert a ½-by- 3-inch lag bolt. For a masonry wall, fasten the rafter plate as in Step 2. 2. Making a template for the rafters. Mark a center line down the face of a 2-by-4. While a helper holds the lower end of the 2-by-4 so that the center line touches the outer corner of the side-wall header, butt the upper end against the house wall with its face against the end of the rafter plate. Hold the top corner of the 2-by-4 level with the top corner of the rafter plate and mark it with a compass: Set one leg against the vertical face of the rafter plate and draw the compass downward so that the other leg scribes a parallel line on the 2-by-4. Take the 2-by-4 down and cut it along the line with a circular saw. Butt the cut end against the front of the rafter plate, and trace the shape of the side-wall header onto the lower end. Extend the lines -- and cut the 2-by-4 along the lines. Then, using the 2-by-4 as a template, mark and cut 4-by-4s into rafters with a circular saw. CENTERLINE; HEADER MARKS 3 Hanging the rafters. Nail a 2-by-4 flat against the house wall at each end of the sun space between the rafter plate and the side-wall header. Then install the 4-by-4 rafters, spacing them every 48 inches on center, their lower ends over the south wall posts. Secure each rafter to the rafter plate with two L-shaped metal hangers. Fasten the two end rafters with an L shaped hanger at the inside and a flat nailing plate over the outside face of the rafter and the end of the rafter plate. Nail the lower end of each rafter to the south wall header. After installing all the rafters, remove the braces from the corner posts. 71 4 Installing roof blocking. Toenail a 2-by-4 — block between each pair of rafters at the south wall header and the rafter plate to form a continuous flat surface as a base for the roof glazing. Angle each section of blocking so that its face is flush with the top faces of the rafters and its outermost corner is even with the rafter ends. Toenail two more 2-by-4 blocks between the rafters to support the bottom edges of the sky lights. Condensation may run down the under side of the roof glazing. To prevent it from collecting on the interior horizontal surface of the south wall header, fill the V-shaped spaces between the blocking and the header with 2-by- 4s beveled to fit, creating a vertical surface that will shed water away from the header. Enclosing a Side Wall Sheathing the wall with plywood. To enclose a side wall, cut 8-foot sheets of ½-inch exterior sheathing-grade plywood to the height of the wall; nail them to the posts, studs and sill plate. Space the nails every 6 inches along the edges of the plywood and every 12 inches elsewhere. Cover the triangular wall section under the roof with plywood cut to size. Over the sheathing, install siding to match the existing house wall. Inside the sun space, staple 4-inch batts of fiberglass insulation to the studs --- 30, Step 2. Finish the interior wall with wall board or plywood. 72 Glazing the South Wall 1 Building frames for glass panels. Place a 1- by-4 spacer horizontally across the outside of the south wall header, setting its top edge flush with the tops of the rafter ends. Nail the 1-by-4 to the header every 16 inches. Cut 1-by-2 spacers to fit vertically between the 1-by-4 and the sill; nail them every 12 inches to the center of every post except the corner posts. Nail a 1-by-3 spacer flush with the outer edge of each corner post. Finally, nail a 1-by-4 horizontally to the sill between each pair of posts, aligning its front edge with the fronts of the posts. Press a length of 1 butyl tape—an adhesive gasket that comes in a roll—around all four sides of the frame. Apply the tape to the posts and header 1/4 inch in from the post edges, and to the bottom 1-by-4 ½ inch up from the sill --. Lay setting blocks—hard rubber pads ½ inch thick and 2 inches long—on the sill, 1 foot on either side of each post. 2 Installing the glass. Strip the paper backing off the butyl tape, and lift a glass panel onto the setting blocks. Push the bottom edge of the panel against the tape, then raise the top into the frame, pressing its edges firmly and evenly against the tape. Hold the panel in place with temporary retaining blocks of scrap wood screwed to the frame through predrilled holes. 3 Securing the panels with battens. Apply a strip of butyl tape to the outside face of each glass panel, V4 inch from the top edge and 3 inches down both sides. Tack 1-by-6 boards across the tops of all the panels, aligning their top edges with the top edge of the 1-by-4 spacer installed in Step 1. Attach the batten permanently with pairs of 3-inch wood screws at 12-inch intervals, 1 inch from its top and 2 inches from its bottom edge. Press strips of butyl tape down the sides of each panel, running the tape 2 inches along the bottom past the corners. Attach a 1-by-4 vertical batten to each post, with 3-inch wood screws located every 12 inches. Finally, apply butyl tape along the bottom edge of each panel, and cover it with 1-inch rounded molding carefully nailed to the sill. 73 Prev | Next: Installing a Glazed Roof |