House Wrap and Foam Board Under New Siding — The Layer That Matters
The siding is coming off anyway, and this is the one chance to put a real weather barrier and some insulation on the wall before it is covered for the next thirty years.
House wrap and foam board under new siding are the layers that keep a Minnesota wall dry and warmer. JMB Builders puts house wrap on the bare sheathing with every seam taped, flashes each window and door in the right order, and adds rigid foam board when you want the wall insulated from outside, with the windows bucked out to meet it. Twin Cities metro, licensed MN contractor BC809005, priced as part of the siding job. Free in-home estimate.
- Wrap taped at every seam, flashed in order
- Foam board sized for a cold-climate wall
- Windows and doors bucked out to the foam
- Quoted as part of the siding job
- Licensed MN contractor BC809005
Send photos and hear back within one business day — or book a free in-home estimate.
Siding does not keep water out. It keeps most of it off, and the wrap behind it handles the rest: wind-driven rain that gets past a lap, meltwater that runs behind a J-channel, the condensation that forms on the back of cold siding in a Minnesota March. On a tear-off job the sheathing is bare for a day, and that is the day the wall gets its weather barrier. Wrap rolled on shingle-style from the bottom up, laps the right way, every seam and every tear taped, and the bottom edge lapped over the foundation flashing so water that reaches it runs out, not in.
The windows and doors are where wrap jobs fail. The order is the whole thing: sill pan or sill tape first, then the window, then the jamb tape over the flange, then the head tape, then the wrap above the window folded down over the head tape. Done backward, every layer dumps water behind the one below it and the wall under the window rots while the siding looks fine. We flash every opening the same way and photograph it before the siding goes on.
Foam board is the insulation question. Rigid foam over the sheathing warms the wall, breaks the thermal bridge at every stud and adds R-value without touching the inside of the house. In our climate the thickness has to be chosen: thin enough that the wall can still dry outward, or thick enough that the sheathing stays warm through winter and never becomes the surface that condensation finds. The middle is where trouble lives. Foam also pushes the siding out, so windows and doors get bucks or extension jambs, the trim gets deeper, and the fasteners get longer. All of that is in the quote when you choose foam.
What you supply
- Photos of the house and a note on what the walls are insulated with now, if you know
- A decision on foam board, after we walk you through the thickness and what it does to the trim
- Your window plan: keeping them, or replacing them while the wall is open
- The siding material choice, since it decides the fasteners and the trim depth over foam
What JMB supplies
- House wrap rated for use behind siding, lapped shingle-style and taped at every seam and tear
- Sill pans or sill tape, jamb and head flashing tape at every window and door, in the right sequence
- Head flashing over each opening and kick-out flashing where a roof meets the wall
- Rigid foam board at the thickness chosen for the wall, seams taped, fastened to code
- Window and door bucks or extension jambs so the units sit flush with the new wall plane
- Furring strips for a rainscreen gap where the siding or the exposure calls for it
- Insect screen and a drainage path at the bottom of any foam or rainscreen cavity
- Photos of every wrapped and flashed wall before it is covered, saved to your job folder
How it is priced: per project
Quoted in writing from your photos, with a reply within one business day. What moves the number:
- Wall area in squares; wrap and foam are both priced by the sheet and the roll
- Foam thickness, which sets the material cost and whether every opening needs a buck
- Number of windows and doors to flash, and how many need extension jambs or bucks over foam
- Rainscreen furring, which adds a layer and longer fasteners
- Roof-to-wall intersections needing kick-outs and step flashing
- Sheathing repair found once the old siding is off
Tell us the wall construction if you know it (2x4 with fiberglass batts is typical for older metro houses). It decides how thick the foam should be.
How long it takes
Wrap and flashing add about a day to a one-story siding job and two to a two-story. Foam board adds another day or two for the bucks and trim.
How your project works
- 1
Send photos, get a written quote
Send three photos of the space and a sentence about what you want. You get a clear, itemized reply within one business day. Prefer a look in person? A free in-home estimate is always an option.
- 2
Pick materials, or bring your own
We help you choose profiles and materials that fit the house and the budget, or match your existing millwork exactly — or you buy the door or trim yourself and we install it. Everything is confirmed before the crew is scheduled.
- 3
Clean, precise installation
The crew shows up on time, protects floors and furniture, and installs with tight joints and consistent reveals. Photos of the finished work go in your job folder.
- 4
Walkthrough and invoice
We walk the finished work with you. If anything is not right, we fix it before we call the job done. Then one invoice, paid by check or direct deposit — no card fees, no payment links.
Situations and options
House wrap only
Wrap, taped seams, full window and door flashing, kick-outs and head flashing. The minimum every tear-off gets. Right for a wall that already has insulation in the cavity and a budget to protect.
Wrap plus foam board
Rigid foam over the wrap or sheathing, seams taped, windows and doors bucked out, trim deepened to match. Adds R-value and stops the stud lines from showing as frost or dust stripes inside.
Rainscreen gap
Furring strips or a drainage mat between the wrap and the siding so water drains and the back of the siding dries. Worth it under LP SmartSide, Hardie or cedar on walls that take weather; vinyl breathes on its own.
Sheathing with the barrier built in
When the old sheathing is bad enough to replace most of a wall, a sheathing panel with the weather barrier on its face can replace both layers. Seams get the system tape and the openings get flashed the same way.
House Wrap and Foam Board Under New Siding — The Layer That Matters: questions, answered
Is house wrap required under siding in Minnesota?
A weather-resistive barrier behind the siding is required to code on new work, and on a residing job it is the whole point of taking the old siding off. Houses from before the nineties often have nothing but tar paper or bare sheathing under the siding. We wrap every wall we strip, tape the seams, and flash the openings into the wrap.
Is foam board under siding worth it on an older house?
On a 2x4 wall with old batts, yes, if the budget allows. The foam adds insulation and covers the studs, which are the cold stripes in the wall. The cost is the foam itself plus the bucks and deeper trim at every window and door. The thickness matters in our climate; we size it so the sheathing stays warm enough or the wall can still dry outward, not somewhere in between.
How thick should exterior foam be in a cold climate?
Thick enough that the sheathing behind it stays above the dew point for most of a Minnesota winter, or thin enough that it does not trap moisture in the wall. The right number depends on the wall framing and the insulation already in the cavity. We will tell you the thickness we would use on your wall and why, and the trim details that come with it.
What is the right order to flash a window into house wrap?
Sill first: a pan or sill tape that laps onto the wrap below and turns up the jambs. Then the window, set in sealant on the sides and top only, never the bottom. Then jamb tape over the side flanges, then head tape over the top flange, then the wrap above the window folded down over the head tape and taped. Each layer sheds onto the one below it. Done in any other order, water ends up behind the flange.
Does vinyl siding need a rainscreen gap?
No. Vinyl is loose on the wall by design and air moves behind it. LP SmartSide, James Hardie and cedar sit tight to the wall and benefit from a drainage gap on walls that take weather, especially the south and west sides and anywhere a roof dumps on a wall. Furring strips or a drainage mat make the gap; a screened opening at the bottom lets it drain.
Will adding foam board change my window and door trim?
Yes. The wall plane moves out by the foam thickness, so the windows either get bucked out to sit in the new plane or stay put and get a deeper trim return. Doors need a buck or a wider jamb so the storm door still fits. Light blocks, hose bib blocks and the meter box all move out too. It is all standard work; it just has to be on the quote from the start.
Recent JMB work, from our job log
59 installs recorded across 30 Twin Cities communities since Dec 2025. Window and door installs for homeowners, builders and dealers. Counts come straight from our job log; no customer names.
Get a written quote for this job
Three photos and a sentence is enough: a reply within one business day, or ask for a free in-home estimate. Or text the photos to 763-333-4066.
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Read morePage reviewed October 2, 2026 · JMB Builders LLC, MN license BC809005 · All siding pages
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