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Existing Walls - Installing STYROFOAM* Residing Board, STYROFOAM Residential Sheathing, STYROFOAM Tongue & Groove, DURAMATE* Plus, TUFF-R* or Super TUFF-R for use as a weather-resistive barrier

Before you put up your new siding, install Dow insulated sheathing right over your old siding and it will go a long way to help you save energy for years. And it makes your home more comfortable. It covers cracks in the walls and gaps around doors and windows. This helps prevent cold air from penetrating your home in the winter and hot, humid air in the summer. What's important too is that the rigid panels give you a smooth, level surface for mounting your new siding. The sheathing is easily installed over existing siding, then new siding, either vinyl, aluminum, fiber-cement, steel or wood is installed according to the manufacturer's recommendations.

Dow insulated sheathing creates the beneficial effect of a warmer wall stud cavity under winter heating conditions, reducing the potential for condensation within the stud cavity. However, where there is evidence of existing moisture related wall problems, corrective actions should be taken before proceeding with new siding application. Corrective actions may include: 

  1. Replacement or repair of rotted siding and trim
  2. Increased attic ventilation capability
  3. Installation of an interior — side vapor retarder

Since each type of siding may require specific application details, consult siding manufacturer's instructions before beginning project. Existing old siding should be in reasonably good condition before residing is started; loose siding should be secured, and all rotted siding, trim, sills, corner-posts, etc. should be repaired or replaced. Remove all gutters, downspouts, shutters, molding and old caulking around windows and doors.

Installation of foam sheathing as a weather-resistive barrier:

1. 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.

2. 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.

3. 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.

man installing STYROFOAM

 4. The new siding is applied in accordance with the manufacturer's instructions. Make sure that mechanical fasteners are long enough to penetrate both the Dow insulated sheathing and the normal securing substrate to a depth recommended by the siding manufacturer.

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. 

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.

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.

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).

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.