Foam Over OSB - Installing STYROFOAM* Residential Sheathing, Tongue & Groove, Square Edge, DURAMATE* Plus, TUFF-R*, Super TUFF-R* or THERMAX* for use as a weather-resistive barrier
1. Install Dow insulation boards over OSB vertically with long joints butted tightly together. The insulation foam board joints should be staggered relative to structural sheathing (OSB or non-insulated sheathing) joints.
2. Secure Dow insulation boards using 1 3/4" ring shank nails or staples with a 1” diameter plastic cap or equivalent fastener long enough to penetrate framing a minimum of 1”. Nails or staples should not be over-driven. Secure the 4’x 8’ and 4’x 9’ boards 12" o.c. around the perimeter and 16” o.c. in the field or as required by the code authority having jurisdiction. Secure 2’x 8’ boards 12” o.c. on each stud (3 fasteners per stud) or as required by the code authority having jurisdiction.
3. Tape all insulation joints and penetrations using nominal 3” STYROFOAM* All-Purpose Tape (ie. horizontal and vertical seams as well as exterior penetrations from pipes, dryer vents etc.). In the case of exterior penetrations only, seal around opening with an all-weather sealant (ie. silicone caulk, Dow GREAT STUFF™ Gaps & Cracks sealant) prior to taping.
4. For window installation the nailing flange is set against a silicone bedding and fastened to the framing with 1½” galvanized roofing nails, 3” from each corner and 8” on center. A 3” wide butyl flashing can be used to seal the sill of the window and a 2” wide butyl flashing can be used to seal jambs and heads. Refer to window manufacturer’s instructions for proper window installation.
Use a utility knife and straight edge to trim the insulation board to conform to irregular wall angles, projections or wall surfaces less than board width or height.
In stick-built construction, consider using 4' x 9' insulation boards to effectively cover the sill plates, floor/ceiling junctures, band box and headers in one easy application.
Brick, wood, hardboard, aluminum or vinyl sidings are fastened to the wood frame construction through the insulation in accordance with the siding manufacturer's instructions.
Shakes or shingles can also be applied by installing furring strips or a plywood nailer base over the insulation and attaching the shakes or shingles in accordance with the manufacturer's instructions.
NOTICE: No freedom from any patent owned by Dow or others is to be inferred. Because use conditions and applicable laws may differ from one location to another and may change with time, Customer is responsible for determining whether products and the information in this document are appropriate for Customer's use and for ensuring that Customer's workplace and disposal practices are in compliance with applicable laws and other government enactments. Dow assumes no obligation or liability for the information in this document. NO WARRANTIES ARE GIVEN; ALL IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE ARE EXPRESSLY EXCLUDED.
NOTICE: Changes to the International Residential Code (IRC) require the installation of a weather-resistive barrier within most exterior wall assemblies in residential construction. The following Dow insulated sheathing products qualify as a weather-resistive barrier (WRB) when installed according to the installation instructions developed for “installation of foam sheathing as a weather-resistive barrier”: STYROFOAM DURAMATE* Plus, STYROFOAM Residential Sheathing, STYROFOAM Tongue & Groove, STYROFOAM Square Edge, STYROFOAM Residing Board, THERMAX*, TUFF-R* and Super TUFF-R* and therefore do not require the use of a building paper or a housewrap as a WRB. When a WRB is not needed, these Dow foam sheathings may be installed according to standard installation instructions for foam sheathing from Dow. Be sure products and installation instructions meet code requirements for your particular location.
Note: STYROFOAM WEATHERMATE* and STYROFOAM WEATHERMATE Plus housewraps have already qualified as weather resistive alternatives to the prescribed felt (see Evaluation Reports NER 593 and NER 640 for approved alternate).
STYROFOAM Extruded Polystyrene Insulation and Dow Polyisocyanurate Insulation
COMBUSTIBLE: Protect from high heat sources. Local building codes may require a protective or thermal barrier. For more information, consult MSDS, call Dow at 1-866-583-BLUE (2583) or contact your local building inspector. In an emergency, call 1-989-636-4400.
THERMAX Products
COMBUSTIBLE: THERMAX products should be used only in strict accordance with product application instructions. THERMAX products, when used in a building containing combustible materials, may contribute to the spread of fire. For more information, consult MSDS and/or call Dow at 1-866-583-BLUE (2583). In an emergency, call 1-989-636-4400.
Building and/or construction practices unrelated to insulation could greatly affect moisture and the potential for mold formation. No material supplier including Dow can give assurance that mold will not develop in any specific system.
