A rear addition, still flat
The pale sheet is the existing house, and the rectangle on the back is a simple rear addition. Scroll to watch that addition go up in the order a wood-frame shell is usually closed in a wet Pacific Northwest winter.
Good Steward Tools
A rear addition, built as you scroll
A one-story rear addition closes in on the back of an existing house, from the footing to the siding. It is a teaching model from the Board of Project Stewardship for homeowners who want to see why the weather layers go on in a particular order in a wet climate.
Illustration only · not a permit drawing
Part of Good Steward. This page does not measure your house. Floor Plan to 3D can check a dimension written on a plan you already have. The Pascal Editor walkthrough covers taping the rooms and drawing them to those numbers.
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The drawing
A rear addition, still flat
The pale sheet is the existing house, and the rectangle on the back is a simple rear addition. Scroll to watch that addition go up in the order a wood-frame shell is usually closed in a wet Pacific Northwest winter.
Scroll to build the addition. The page still scrolls normally on a phone.
Motion is reduced, so the model holds the stage you pick. The full sequence is written below.
Footing and foundation tie-in
The new footing is dug to firm soil and tied into the existing foundation, so the addition does not sit beside the house as a separate box. Where the ground stays wet, a drain beside the footing and a cover over the crawlspace soil keep damp soil air from becoming the new floor's problem.
Floor framing
Joists span from a ledger on the existing house to the new wall, then a subfloor closes the crawlspace. A capillary break under the mudsill keeps concrete moisture out of the lumber, and the crawlspace still has to be able to dry.
Wall framing
Studs, plates, and headers stand up next and carry the roof and the window and door openings. The new walls have to fasten into the existing house, so wind has a path into the older structure and not only into the fresh lumber.
Sheathing and weather barrier
Sheathing stiffens those walls, then a weather-resistive barrier goes on the outside, lapped so water runs down and out. The wall is expected to get wet in this climate, so a gap stays in front of that barrier for water to drain before the siding covers it.
Roof framing and roofing
Rafters, roof sheathing, underlayment, and the roofing close the top before the walls are finished on the outside. Where the shed roof dies into the existing wall, apron flashing goes in so the barrier above can lap over it, and a kick-out at each end turns water onto the roof instead of into the corner.
Windows and doors with flashing
The door and windows go into flashed openings: a sill pan first, then the unit, then side flashing, then head flashing that laps over the weather barrier. Reversing that order lets wind-driven rain run in behind the trim.
Siding and trim
Siding and trim finish the rain screen, and the gap behind the siding lets water that gets past the cladding drain and dry. The siding stops above grade so the bottom edge is not sitting in splash water from a wet Pacific Northwest yard.
What you are looking at
The existing house stays put. The addition is a crawlspace with wood joists, stud walls, a weather-resistive barrier, a shed roof that dies into the old wall, flashed openings, and siding held off the barrier. That is a common one-story rear addition in this region. A slab, a basement, or a second story is a different assembly.
Layers in the model are drawn thicker than real materials so the rain-screen gap and the flashing can be seen. Nothing in the model is uploaded, and there is no file to download. It is not a bid, a structural calculation, or a permit set.
Read home addition planning before you hire, and coastal waterproofing for the same wet-wall habits on an existing house. The Build Walkthrough is the longer homeowner checklist from sale through handoff.
Rear addition sequence FAQ
Is this model a construction document?
No. It shows one common one-story rear addition: a crawlspace, wood framing, and a shed roof that dies into the existing wall. Soil, roof shape, and the existing house can call for a different assembly. Permit drawings come from the designer, engineer, and contractor after they measure the site.
Why this order?
The shell is closed against rain before the finish layers. The roof and the flashed openings depend on the weather barrier being in place so each layer can lap the one below it. Crews overlap these stages on a real job. The model separates them so the laps are easier to see.
What does the model leave out?
Insulation, interior finishes, wiring, plumbing, and heat. It also leaves out grading that carries yard water away from the house. Layers are drawn thicker than real materials so the gap and the flashing can be seen.
What if scrolling is difficult?
The stages are written in order under the model. Choose a stage and the model jumps there, with no animated scroll. The same list is what you get when the browser asks for less motion.
Board feature
Another Story
Same home. Another story. Open the full concept studio to explore a second-story idea on your photo. Concept preview only, not a bid or permit document.