Gibson St shed · two west-wall salvage sash · redesigned September 11, 2026 · current layout plus retained research history
Purpose of this page. Windows Explained teaches the vocabulary. This page records the actual installation and wall-drainage discussion: what JCS specified, what the modified wall now requires, which ideas were explored, what has been rejected, and what remains to choose.
All four pieces around each opening stay at the full 3½-inch depth: two full-height window studs, sill and header. Ordinary girts and non-window studs are ripped to 2¾ inches.
MeasuredConfirmed RO width: 34 inches. The older record lists sash 33½ × 19⅛ inches and RO height 19⅝ inches; retain those sash figures as recorded, not a new measurement. RO height is NOT a final cutting instruction: the sill can move to accommodate the finished drainage/support stack. Do not enlarge the confirmed width based on stale entries.
SettledThe 0.451-inch liner covers the ripped framing. Full-depth window framing remains proud of the liner by about 0.30 inch, matching the exposed posts.
Current directionThis page now develops both sash as fixed, service-removable units—not hinged windows. Interior stops locate them; screwed exterior stops retain them. Top-and-side weather sealing and intentional drainage below remain the direction. Opposing screened gable vents remain the ventilation proposal.
Still openWindow construction (sill/pan, stops) is still not finalized, and the sash still need rehab (see Window Restoration).
Decided (Oct 1, 2026): CSSB-compliant #30 felt, cap-stapled, bought later from a roofing supply house (about 2 rolls); no seam tape. A drainable WRB is no longer an option. The finalists are CSSB-compliant #30 felt or a named drainable WRB. A ¼-inch mesh and crossed-furring rainscreen are technically robust but poor cost/complexity fits.
Current direction: flexible membrane over beveled wood on a level structural sill. The user does not want to fabricate an aluminum tray. Visible sill cover, membrane system, support-block sizes and rear-edge detail remain unresolved—not ready-to-cut dimensions.
Dimension correction preserved. Earlier discussion confused sash dimensions with RO dimensions and produced a 34½ × 20⅛-inch opening. Those figures are superseded. The 34-inch RO width is confirmed. Final height must include slope backing, flashing, support blocks and sash clearance; do not treat the old 19⅝-inch height as fixed.
The purchased Jamaica Cottage Shop plans use vertical board-and-batten siding and provide a very simple barn-sash installation. They specify a rough opening ½ inch larger than their nominal sash, 1×3 stops flush with the interior face of the framing, exterior 1×4 casing, top hinges, and an outward/upward-opening sash.
They do not detail exterior plywood, an interior liner, WRB, sill-pan flashing, jamb flashing, a head-flashing sequence, a sloped sill, a drainage cavity, or concealed-water inspection. Those omissions are understandable in the original board-wall system: leakage is visible and the wall can dry readily.
Why the modified shed needs more. Exterior plywood + underlayment + shingles + interior plywood create concealed layers. A small window leak can remain unseen against the sheathing. The objective is therefore not a magically leak-proof sash; it is a drained opening that makes incidental leakage harmless.
This is an adaptation of the JCS shell, not a JCS window-installation detail or a proprietary tested window system. The purchased plans remain the source for the original construction. This page separates confirmed preferences from proposed details and unresolved sizing.
These salvaged units are wooden, glass-bearing sash—not complete replacement windows with surrounding frames or mounting flanges. The opening framing and added stops provide that missing surround. Fixed installation removes hinges, hooks and operating-sweep requirements. The user expects to open the doors when working inside rather than leave windows cracked unattended; opposing screened gable vents remain the passive-ventilation proposal. Returning to an operable sash would require revisiting retention, weather seals and clearances.
| Component | Job and location |
|---|---|
| Interior stops | Fixed strips at the top and sides, behind the sash. They establish its inward limit. Their position follows the sash—not automatically the interior wall face. |
| Exterior retaining stops | Separate removable strips INSIDE the RO, attached to the jambs/header with accessible screws. Their exterior faces align with the exterior plywood face. They overlap the sash's wooden perimeter, not its glass or glazing putty. |
| Decorative exterior casing | The larger picture frame around the opening. It covers the wall/opening transition and meets the shingles. It does not have to touch or retain the sash. |
| Bottom support blocks | Carry sash weight above the drained membrane, provide level bearing, and leave drainage paths between supports. Sizes and locations require final sash/sill geometry. |
| Finished sill | Sloped visible weathering surface/cover, projecting beyond the siding below. This is separate from the level structural sill and the concealed waterproof membrane. Final cover profile remains open. |
The user's simpler proposal is adopted: the exterior stops sit within the opening, their outward faces flush with the plywood sheathing plane. They screw into the surrounding opening framing. They do NOT straddle the plywood face like face-mounted battens.
Sash exterior-face setback from plywood = retaining-stop depth + compressed bedding/gasket thickness.
An illustrative ¾-inch stop depth puts the sash face roughly ¾ inch behind the plywood, plus bedding. This is an example, not a selected stop size. "Depth" here means front-to-back; it is not the strip's visible width or overlap onto the sash.
The sash is not required to be centered in the 3½-inch frame. Check that sash thickness, both stops and bedding fit the available opening depth. Do not fix the interior stops flush with the interior wall merely because the original JCS detail did.
The sash is inserted from outside, seated on bottom supports and against the interior stops/bedding. The exterior retaining strips are then fitted and screwed to the jambs/header—not through the old sash. The screws must remain reachable, and the strips must have a removal path not trapped by casing or shingles. Screw angle, length, spacing, stop section and wood edge distances are still to be specified; this is not a fastening schedule.
"Removable" means serviceable, not operable or loose. Removing these strips lets the sash come outward for glazing repair, glass replacement, painting, gasket replacement or sill inspection. Do not permanently glue the strips in place. Sealant bridging a removable joint must be cut and renewed at service. The head casing and its flashing should remain undisturbed.
Do not clamp hard enough to distort the sash or stress its glass. Maintain installation clearance. Top-and-side bedding limits rain entry, but is not a substitute for flashing. A separate interior-side air/water seal must be detailed without obstructing the exterior drainage outlet.
The bevel creates the slope; the membrane creates the waterproof layer. Neither is the finished visible sill. Avoid fasteners through the drainage floor. Include every layer and support height in the RO-height calculation before fixing the structural sill.
A single beveled board across the 34-inch opening is preferred for a smooth, continuous backing. Carefully fitted cedar shingles remain an alternative: thick ends inward, thin ends outward, side by side with matching slopes—not overlapped as roofing courses. Secure backing before covering it with membrane. Avoid unsupported joints, sharp edges and abrupt steps.
A short piece cut from a long shingle retains only the taper over that short distance; it does not give the full butt thickness as a drop. The older approximate ¼-inch drop across the sill was a planning target, not a selected membrane manufacturer's requirement. Actual bevel, available height and membrane instructions must be reconciled.
A back dam, if used, is at the INTERIOR side of the sash, not a curb outside it. It keeps water beneath the sash from continuing indoors. A strip of wood wrapped with membrane can form one; folded metal is not necessary.
End dams are the side upturns beside the jambs. In this version, membrane turned up both jambs forms the side containment. Corners need the selected product's formable membrane or compatible corner patches; a wrinkle or unsupported bridge across a corner is not a watertight detail.
Correction: Building Science describes a back dam OR positive outward slope. A separate raised back dam is not universally mandatory for every sloped detail. That does not waive a chosen membrane system's requirements. The rear termination/interior seal still needs an explicit detail. Do not assume an interior stop hides an upturn; it may require a deliberate groove or cover.
The exterior front stays open to drain over the lower WRB. Bottom supports and any bottom retention must not create a continuous blockage. "Seal top and sides" does not mean leave an uncontrolled path into the room; interior sealing and exterior drainage occupy different positions.
The latest candidate is cedar beveled siding, approximately 3–4 inches deep after trimming away its thinner portion. Keeping the thicker portion may improve strength, but does not establish sufficient thickness for concealed screws without exposed tips. Small clearances at the jambs and sash were proposed; these alone do not provide drainage if the underside traps water against the membrane. Water beneath a cover must be able to drain outward and the assembly must be able to dry.
Bracket/cleat-supported floating covers and a thicker solid cedar finish sill were explored, but neither is an adopted attachment detail. Do not build from those suggestions. A thicker finish sill, if pursued, would NOT replace the confirmed sloped backing beneath the membrane. Do not glue or caulk a cover down in a way that dams the drainage route, or improvise fasteners through the pan floor. Resolve the complete section before cutting or attaching the finish piece; keep sash support independent of a removable cover.
A simple head drip cap is a different component from an aluminum sill tray. Avoiding the latter does not eliminate head flashing.
The original JCS page 31 detail puts casing over flat board siding. The modified guide says shingles terminate at trim but lists shingles before trim. That did not resolve the new assembly. For this design, install casing on flat, flashed backing over plywood, then fit surrounding shingles to it. Do not seat flat casing over the ridges of overlapping shingles.
| Wall field | At casing |
|---|---|
| Framing → plywood → felt/WRB → shingles | Framing → plywood → integrated WRB/flashing → solid packer if necessary → casing |
Felt is a weather layer, not fastening support. Attach casing into suitable solid wood backing through the intervening layers. Preserve the opening's flashing and drainage routes. With a separate drainage mat, account for its thickness and provide firm trim support rather than crushing mesh beneath casing.
Shingles terminate beside the casing's outside edge with the applicable movement clearance—not jammed tight, and not run behind the casing. The casing can conceal the opening-to-wall transition without trapping the removable retaining strips.
Nominal 1×4 casing is not a complete thickness specification. A surfaced board may be ¾ inch thick; actual cedar products vary. Overlapping shingle courses create a varying built-up profile, not just one butt thickness.
Target the casing face flush with or slightly proud of the thickest adjacent shingle profile. Use thicker casing or a solid packer as needed. Compare actual trim against a small sample of overlapping courses at the intended exposure, including any drainage layer. The earlier blanket statement "felt requires no trim buildout" was not justified.
A head flashing over the head casing must intercept water from above and discharge beyond its face. Integrate its rear leg behind the upper WRB and coordinate its ends with the jamb protection. Rough-opening tape alone is not the cap protecting the top of the casing.
CSSB's sidewall manual calls for ½-inch clearance above surfaces below to avoid wicking; preserve that drainage/clearance above the head flashing. Do not caulk the outlet shut. A projecting finished sill likewise sheds water beyond the siding/trim below, while the concealed membrane retains its own open drainage route.
The same casing-depth question applies to doors and corner boards. Existing trim quantities, stop stock and fastener lengths were not recalculated for this redesigned fixed window. Do not treat the old 1×3 stop purchase allowance as a verified takeoff for both sets of stops. No framing width change is implied; header position stays as intended, and the structural sill height remains adjustable.
Retained for reference only. The following fabrication notes describe the earlier option; they are NOT instructions to build the current window. The user prefers a membrane-based pan because tight metal folds and fit feel impractical.
A pan can be made from factory-painted aluminum trim coil or sheet. Use approximately 0.019-inch minimum thickness; 0.024 inch is preferable if available. Very thin disposable flashing roll is easier to dent and crease.
A local gutter/siding shop can brake-form the long bends cheaply if the three-dimensional end folds prove difficult. A shop bend does not eliminate the need to inspect and test the corners.
cedar shingles→underlayment face→bottom flashing→outside
Water behind cedar shingles is expected occasionally. The underlayment is supposed to stop it from reaching plywood and direct it down its exterior face. Both felt and housewrap can serve as that drainage plane. A physical gap or textured wrap improves drainage/drying; it is not what first introduces water behind the shingles.
Cedar tannins and wood sugars can act as surfactants and reduce the water repellency of some sheet WRBs, particularly when wet cedar is held tightly against them. That is the durability argument for standardized felt, a named surfactant-resistant/drainable WRB, or a physical rainscreen gap—not a claim that ordinary housewrap is categorically forbidden.
CSSB does not require plastic rain mesh. Its current sidewall guidance recommends No. 30 felt conforming to ASTM D226 Type II or ASTM D4869 Type IV. USDA/FPL guidance also recognizes locally approved housewrap. Drainable WRBs and mesh/furring are enhanced options.
| Assembly | Approx. shed cost | Trim / fastener impacts | Assessment |
|---|---|---|---|
| #30 felt → shingles | ~$72 2 × 200-sf rolls | No added drainage-layer buildout; casing depth and nail length still require checking; no field seam tape | CSSB-standard, least expensive. Flashing integration with building paper requires deliberate aprons/bibs/laps. |
| Generic smooth housewrap → shingles | ~$136 wrap + tape | Little WRB buildout; casing depth and fasteners still require checking | Not prohibited, but the original “Tyvek or similar” specification is too vague for direct cedar contact. |
| Drainable WRB → shingles | ~$210–257 HydroGap-class roll + system tape | ~1 mm profile; still verify casing depth and fasteners | Best middle path: named system, small drainage channels, simpler window integration. |
| Felt + ¼-inch mesh → shingles | ~$730–812 | About $100 of solid ¼-inch packers behind ~136 lf of 1×4/1×5 trim; top/bottom insect screening; deeper flashing projections | Best drying, but poor value and much more detailing for this shed. |
| Wrap + ¼-inch mesh → shingles | ~$794+ | Same trim packout and screening | Robust but not recommended on cost/complexity. |
| Crossed wood-furring rainscreen | ~$600–900+ | ~1½-inch exterior buildout; new jamb/casing extensions; materially altered wall geometry | Eliminate from this project. |
Historical pricing, not current quotes or a final order: APOC felt ~$36.24/200 sf; generic wrap ~$118; HydroGap 5×100 ~$185–217; Slicker Classic ~$176–197/150 sf, three rolls; packers based on two ¼-inch exterior-glue plywood sheets. Tax, shipping and flashing common to all options excluded.
Whatever underlayment is selected, upper layers must overlap lower layers. Water cannot be asked to travel uphill, and the pan outlet cannot be sealed shut.
upper underlayment→head flashing→jamb flashing→pan end dams→sill pan→lower underlayment
This is the construction order for the selected concept, not permission to mix unrelated flashing products. Follow the selected membrane system's lap and substrate requirements.
This is a detail for the modified plywood wall, not the original JCS board-siding system. The west-wall W2 and W4 panels may be installed as solid rectangles over the window locations and opened after the roof is on. As of Oct 1, 2026 W2 and W4 are still solid sheathing, to be cut out later. This avoids lifting a full-height panel with only narrow plywood webs remaining beside a precut 34-inch opening.
| Operation | Preferred tool |
|---|---|
| Create an undersized access opening | Circular saw or jigsaw |
| Cut accurately to the installed framing | Compact trim router with a bottom-bearing flush-trim bit |
| Square the four rounded corners | Oscillating multi-tool |
| Make small corrections | Oscillating multi-tool or sharp chisel |
Recommended sequence:
Use a small laminate/trim router rather than a full-size router for easier control on the vertical wall. Do not use a reciprocating saw: its blade can wander behind the plywood, damage the exposed window framing and leave too little of the narrow side webs for reliable fastening. Wear eye, hearing and dust protection, and practice the router operation on a plywood-covered scrap frame if it is unfamiliar.
Do not simply cover the wall with one sheet and leave raw cut edges around the window. The published building-paper method uses a loose sill apron, separate jamb paper pieces, corner patches, jamb/head flashing, and later field courses tucked or lapped shingle-fashion. Ordinary horizontal felt laps are not seam-taped; localized flashing still is.
GCP Vycor Plus 6×75 (~$38) was the best-supported readily available flashing found: GCP lists PT wood, plywood and metal as suitable substrates and asphalt felt as chemically compatible. However, chemical compatibility is not a guarantee of strong adhesion to every rough felt surface. Critical bonds should be to clean structural substrates/metal, with felt integrated by laps rather than relying exclusively on tape-to-felt adhesion.
Use one named manufacturer family for WRB, sill/corner membrane, jamb/head tape and compatible sealant. Follow that system's illustrated sequence. This avoids inventing a hybrid detail between asphalt felt, unrelated tape and a custom pan. Confirm in writing that the selected WRB is approved in direct contact with the exact cedar shingle finish—especially if the shingles remain unfinished.
Sealant is a first defense, not the drainage system. Do not run a continuous exterior bead across the bottom in a way that turns the pan into a bathtub. Any sealant touching rubberized-asphalt flashing must be confirmed chemically compatible.
| Idea | Status and reason |
|---|---|
| Rip the window studs/sill/header to 2¾ inches | Rejected. Full-depth opening framing provides solid sash/stop attachment and the intended exposed 0.30-inch reveal. |
| RO exactly equal to sash | Rejected. JCS uses ½-inch total installation clearance. Current measured RO/sash already honor that rule. |
| 34½ × 20⅛-inch RO | Superseded. It resulted from confusing the current RO dimensions with sash dimensions. |
| Tilt the entire structural sill | Rejected. Keep framing square; create drainage slope in the pan support/detail. |
| Exposed flashing tape as finished sill | Still rejected. Current membrane needs a resolved protective finish, not necessarily a metal tray. |
| Wood finish sill over membrane pan | Reopened for the current design. Thickness, durability, fastening and drainage must be resolved. |
| Custom pan requires an engineer/shop | Rejected. DIY trim-coil pan is feasible if folds and water test succeed; shop brake-forming remains an inexpensive fallback. |
| Interior stop automatically hides pan back dam | Wrong. Explicitly resolve rear termination and any visible upturn. |
| Exterior stops straddle the plywood face | Superseded by jamb/header-mounted strips INSIDE the opening, outward faces flush with sheathing. |
| Sash must remain flush with plywood or centered in frame | Neither required. It is recessed by exterior-stop depth plus compressed bedding. |
| Casing doubles as removable sash retention | Not the selected arrangement. Keep decorative casing and accessible retaining strips separate. |
| Separate raised back dam always required | Too categorical. Positive slope may serve under the cited guidance; chosen product requirements and interior termination govern. |
| Shingles first, then casing over them | Superseded. Flat-backed casing precedes the adjacent shingle work. |
| Rain mesh required by CSSB | Wrong. Mesh is optional enhanced drying; CSSB's standard direct sidewall assembly uses compliant #30 felt. |
| Housewrap forbidden behind cedar shingles | Wrong. It is not categorically prohibited; the exact product/direct-contact suitability matters. |
| Full crossed-furring rainscreen | Eliminated. Excess cost and ~1½-inch trim/opening redesign. |
PLANS.GBL.10X12.SHELL.pdf) — original stops, casing over board siding and hinged sash; not the modified membrane installation.