A common problem is caused when the original slope of a roof changes, causing water to either drain in the wrong direction, or to begin ponding. When this occurs, the slope of the roof can be corrected easily with the use of perlite lightwieght concrete.

Perlite concrete can be used as a thin (0-4 inches) fill to correct slope to drain problems, it can be poured over irregular substrates, and it often can be installed directly over B.U.R. and gravel roofs (eliminating costly tearoffs.) And because it is so light, the addition of a perlite concrte layer does not substantially add to the overall wieght of the roof. In fact, in many of these applications, perlite concrete simply is placed over the existing roof to correct slope problems, and then new insulation (sometimes a perlite concrete deck) is placed directly on top.

What is perlite concrete?

Perlite concrete aggregate combined with portland cement and water produces a lightweight insulating concrete used for lightweight roof decks, floor fills, lightweight structural decks, insulation for steam and coolant lines, bases of cryogenic storage tanks, oven insulation, interstitial spaces in reconditioned water and sewer lines, interstitial floors in hospitals, lightweight pre-cast forms and blocks, statuary, basic fills, and many other applications where a lightweight permanent concrete is desired. Although many uses could be described in greater detail, the most common and well-established uses have been for insulating flat roof decks and for repairing existing roofs.

The physical properties of perlite concrete vary according to mix designs. Perlite concrete can be made with a dry density of 20 lb/ft³(320 kg/m³) or with the addition of sand or other aggregates up to 90 lb/ft³ (1440 kg/m³). The lower the density, the higher the insulating value. For most uses to maintain a proper balance between insulation value and compressive strength, a 1:6 (one part portland cement by volume to 6 parts perlite by volume) mix is chosen with a density between 24-30 lb/cf³ (384 and 480 kg/m³). This provides a k factor range of 0.58 to 0.66 Btu-inch/h-ft2-F (0.085 to 0.095 W/m-k) and a compresssive strength of 125 to 200 psi (986 to 1378 Pa). For specific applications requiring higher strengths or other special properties, consult a local perlite manufacturer or The Perlite Institute.

ROOFING INSULATION

Perlite concrete roof deck insulation is an ideal base for built-up and single ply roofing systems. It has superior wind and fire resistance over other roof insulation materials and with the addition of polystyrene insulation board sandwiched in the perlite concrete, high thermal resistance values are economically achieved.

Positive drainage is easily accomplished by varying the thickness of perlite concrete or by stair stepping different thicknesses of polystyrene insulation board and then covering it with a uniform layer of perlite concrete.

Perlite concrete insulation may be placed over vented or slotted galvanized steel decking, precast or pour-in-place concrete, or existing roofing materials providing a seamless, smooth, and hard surface ready for roofing. If exposed to water it will not deteriorate.

REROOFING BASE

Perlite concrete insulation is ideally suited for reroofing applications. It provides permanent, cost effective, slope-to-drain designs with high R-values over flat and often-irregular substrates found in reroofing projects. Using a perlite concrete slurry coat, the polystyrene insulation board is positively attached to the substrate and covered with a uniform layer of perlite concrete insulation. If the existing substrate is sound and capable of the additional loading required, then the perlite concrete insulation can be applied to the existing roof thereby eliminating costly tearoffs.

TESTING AND APPROVALS

Perlite roof deck insulation systems have been tested and approved for wind and fire ratings by Underwriters Laboratories, Factory Mutual, and of the code authorities. The system is rated as non-combustible by Factory Mutual. U.L. Design P-920 successfully achieved the fist 2-hour rating for any system of this kind under full-scale fire conditions. Perlite concrete roof decks with polystyrene insulation board meet the criteria for U.L. Class90 and FM I-90 wind resistance.

CODE APPROVALS AND GUIDE REFERENCES

• International Conference of Building Officials (ICBO)
• Building Conference of America (BOCA)
• Southern Building Code Congress (SBCC)
• South Florida Building Code
• Ferderal Construction Guide Specification FCGS 03501
• U.S. Army Corps of Engineers Guide Specificatoins: CEGS 03510

TECHNICAL SUPPORT

• FM I-90 Wind Uplist
• FM Serial Report No. OC2AO-AC
• U.L. Wind Uplift Construction No. 143
• U.L. Wind Uplift Construction No. 250
• U.L. Fire Rated Designs