Wire, nails, screws and other insulation fasteners for rigid foam boards, blankets and batt insulation installation

Fasteners can be a key element when installing blanket and batt insulation in underfloor spaces, or when installing rigid insulation panels or equivalent materials on basements or on exterior walls, or even when sealing and insulating ducts (mastic doesn't hold ducts together; we have to use mechanical fasteners to get it).

In most cases, insulation fasteners are basically a way of holding insulation in place, but that doesn’t mean that it isn’t important. It determines the quality of the installation, which is greatly determines its success.

Typical insulation fastener products

Insulation fastening for concrete and wood framed walls include:

- Fastening furring and plastic strips,
- long framing nails (often installed with a nail gun) and long ring-shank nails and
- insulation screws.

Insulation wire fasteners is another and very different type of insulation fastener, for underfloor spaces, as mentioned below.

Insulation wire fasteners for underfloor spaces

You may use the friction fit method to hold the insulation in place. That is: you should expand the insulation to its full thickness in the join cavity, insuring complete coverage and allowing friction to hold insulation in place.

Just avoid compressing the material; the most effective way of permanently holding the insulation material in place is to use wire fasteners – straight, galvanized, rigid wire fasteners with pointed ends.

These insulation fasteners are specifically made for common joist spacing, that is, 12-16-18-20-24 inches, and can be used against several materials (wood, but also concrete or metal).

The fasteners should be slightly longer than the joist spacing where they are going to be installed.

They should be bowed upwards into the insulation material, to press the insulation into contact with the subflooring.

Be sure that the insulation fasteners do no compress too much the material; that would reduce its R-value. Also space the fasteners properly, to prevent sagging. Typically they are spaced 12 to 24 inches apart. Also do not place them too close to the ends of the insulation material; place the insulation fasteners at least 6 inches from the ends.

Using insulation fasteners in basement walls in unvented crawl spaces

Unframed-exterior basement walls are often insulated with blanket insulation materials – horizontally or vertically installed.

Usually, the blanket insulation material is held against the sill plate (at the top of the wall), by using furring strips.

But furring strips are not enough to hold the blankets in place.

You may also need patch tape, and in many cases special mechanical fasteners for driving into concrete or other material of the wall assembly.

Insulation adhesives  

Adhesives or adhesive applied stick-pins can be a good option for temporary attachment of rigid foam boards or mineral wool insulation, but not for permanent attachment.

This one requires mechanical attachment or an equivalent method.

Insulation fasteners for exterior wall insulation with rigid foams and mineral wool

Typically, exterior wall insulation involves rigid foam or mineral wool insulation and furring strips; but there are other less common products like panels of expanded polystyrene (EPS) foam with embedded plastic elements that hold drywall screws…

Whatever the insulation material, fasteners – proper nails and screws - are a key element, though the exact type of fasteners and the fastening system vary with the type of insulation substrate and the different loads to which the insulation material is subject.

Issues like the number of rows of nails and screws or their cross-section vary according to specific conditions, the materials, the weight of the insulation material, the type of siding, the risk of tearing or even with meteorological conditions. Consider the manufacturer instructions.

Insulation plastic cap nails and metal screws

Typically, to fasten rigid foam boards to wooden studs, we use broad-headed fasteners – mostly plastic cap nails (roofing cap nails).

To fasten rigid insulation to metal studs, instead of plastic nails, builders use mostly sheet metal screws with rubber washers.

The insulation fasteners should be long enough; they should penetrate about 3/4 of an inch into the framing.

In some cases, when the weight of the insulation panels is significant, the fasteners must solve two problems: how to fasten the panels securely to a wall, and how to do fasten the siding securely to the panels.

Insulation fasteners for exposed insulation materials

Mineral wool or rigid foam board insulation are not expected to be left exposed to the elements. Builders should install a protective layer after insulation attachment.

But the insulation is sometimes left exposed. In this case some manufacturers often recommend a minimum of 5 mechanically-attached insulation fasteners per standard board – a number that can be increased to meet specific requirements associated to special loads (wind-driven loads or others).

Insulation fasteners for EPS (Expanded polystyrene) panels

Exterior wall insulation can involve rectangles of EPs foam and other less common products, which may involve special fastening systems.

In the case of products like InSoFast EPS foam with embedded plastic elements to hold drywall screws, the fastening process can be complex: besides the polypropylene fastening strips spaced 16 inches on center, the installer should also use special insulation fastening nails (when the temperatures are above 50ºF) or long framing screws (in order to not shatter the plastic strips, in cold weather).

Insulation fasteners thermal effect

We may ask ourselves: what’s the thermal effect of dozens of large nails, screws or other fasteners that penetrate insulation? Doesn’t it degrade the insulation levels (R-value)?

Thermal bridging (unwanted heat transfers wherever there is a penetration of the insulation layer by a highly conductive or non-insulating material) can be a problem, and fasteners can be part of it.

But if given proper care the effect that fasteners have on the insulation value of exterior walls is typically on the order of 1 to 2%. And though it should be taken into account, that’s not a huge problem…

National Institute of Building Sciences
NREL Thermal Impact of Fasteners




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