The Complete Guide to Spray Polyurethane Foam Insulation: Roofs, Metal Sheet (Shinko) Roofs and Hangars

Spray polyurethane foam (SPF) is one of the most widely used insulation systems on villa roofs, warehouses and metal sheet (shinko) hangars in Saudi Arabia, because it is manufactured on site: two liquids are mixed in the spray gun, react and expand within seconds to form a rigid layer bonded to the substrate with no joints and no fasteners. This guide is written for the owner who wants to understand what they are paying for, and for the engineer who wants numbers that can be checked against technical datasheets. We briefly explain the chemistry, then the technical properties, then the thermal resistance calculation for different thicknesses, then application, inspection and common defects, and finally cost and maintenance.

What is polyurethane foam? The chemistry in plain terms

The system consists of two components delivered in separate drums. The first is the isocyanate, which in spray systems is typically polymeric MDI (PMDI). The second is the polyol blend (resin blend), which contains the polyol itself (polyether or polyester) together with catalysts, cell stabilizers, flame retardants and the blowing agent. When the two are mixed at a set volume ratio (usually 1:1 in spray systems) and at controlled temperature and pressure in the proportioner, a polymerization reaction produces polyurethane, while the blowing agent evaporates or gas is generated, forming millions of tiny cells. References note that the mix expands to dozens of times its liquid volume.

A real example from a European datasheet for a closed-cell spray system: component (A) is a «mixture of polyether and/or polyester polyols, stabilizer, flame retardant, catalyst and blowing agent», and component (B) is polymeric MDI with an NCO content of about 31.5%. These details matter: any error in mix ratio or component temperature produces weak, brittle or discolored foam.

The blowing agent: why it matters

The blowing agent is the gas that fills the closed cells, and it is the main reason closed-cell foam has a lower thermal conductivity than air. Historically, HFCs with high global warming potential were used; the industry has since moved to low-impact HFOs such as trans-1-chloro-3,3,3-trifluoropropene, while open-cell systems usually rely on water, which generates carbon dioxide during the reaction. When comparing quotations, ask about the blowing agent and request the product datasheet, because the «aged» thermal value depends on it.

Closed-cell versus open-cell

Closed-cell foam (called «two-pound foam» in the US market, or heavier for roofing) has more than 90% closed cells, so it is rigid, tolerates foot traffic and light loads, and resists water absorption, which is why it is the type used on exposed roofs. Open-cell foam (about half a pound per cubic foot, roughly 8 kg/m³) is soft and light, with thermal resistance of about R-3.8 per inch (conductivity around 0.038 W/m·K). It is used inside walls and protected ceilings and is never suitable as an exterior layer on a roof exposed to rain and sun.

Technical properties: what do datasheets actually say?

The US specification ASTM C1029 (external source via the Consumer Safety Center) is the best-known reference for spray-applied rigid polyurethane used as thermal insulation. It classifies the material into four types (Type I–IV) and requires testing of thermal resistance, compressive and tensile strength, water vapor permeability, water absorption, thermal and humid aging, closed-cell content and surface burning characteristics, covering surface operating temperatures from about −30 to +107 °C. In Europe these products fall under EN 14315-1. The following table summarizes actual figures from datasheets of roofing spray products:

Thermal and waterproofing in one: the truth and its limits

Foam is often marketed as «waterproofing and thermal insulation in one layer», and this is partly true. The sprayed layer is continuous and seamless, it bonds to concrete and metal sheet, the closed cells block liquid water, and water absorption is low, as we have seen. But there are three limits the owner must know:

• UV radiation destroys exposed foam: the surface first darkens, then becomes brittle and friable, then the thickness gradually erodes. Foam alone is therefore not a finished surface.
• Water enters through details, not the field: drains, parapet edges, AC unit bases and pipes are the weak points, and any foam not carefully sprayed there, or covered with a thin topcoat, will allow leaks.
• Foam is not an absolute vapor barrier: its water vapor permeability is low but not zero, so cold stores need attention to the correct vapor barrier in the design.

This is why an engineer treats foam as a system of at least two layers: foam at a calculated thickness, and a flexible topcoat at a specified dry thickness. If the roof has existing leaks or structural cracks, treatment comes before spraying; see concrete repair and leak detection before making a decision.

The UV-protective topcoat: mandatory, not optional

The roofing guide published by IBHS (external source via the Consumer Safety Center) lists five main types of foam topcoat: acrylic, butyl, silicone, polyurethane and polyurea, and requires all of them to be elastomeric, capable of at least 100% elongation. It stresses that unprotected foam first discolors, then becomes friable and loses thickness.

Application details stated in manufacturer guides: the first topcoat layer is applied on the same day as the foam unless weather prevents it, with at least 12 hours between coats and a minimum of two coats. One application guide sets a minimum total dry film thickness of 22 mils (about 0.56 mm) for its system; the thickness required for your project is whatever the datasheet of the chosen topcoat specifies. The rougher the foam surface, the more coating is needed to cover the peaks.

Applications: concrete roofs, shinko roofs and hangars, and cold stores

Concrete roofs of villas and buildings

This is the most common application. Foam is sprayed directly onto the slab after it has been cleaned, dried and its cracks treated, and then the topcoat is applied. Its advantage here is that it covers slopes and details without joints, and thickness can be varied to improve falls towards drains. Compare this option with other systems in the complete roof insulation guide and on the roof insulation service page.

Metal sheet (shinko) roofs, warehouses and hangars

Metal sheets heat up strongly in the sun and transfer heat quickly inside, and water usually leaks through fasteners and side laps. Foam covers all of this in one layer and reduces rain noise; it is sprayed either from the outside (with a topcoat) or from the inside beneath the sheets. Two points to note: metal is a «heat sink» substrate, so some datasheets require special techniques such as a thin first flash pass, and rust must be removed and treated before spraying. For interior spraying, fire protection requirements are stricter, as explained below.

Cold stores and refrigerated rooms

The density and closed cells of foam make it suitable for insulating cold rooms, but the design here is purely engineering: the vapor barrier must be located on the warm side, thickness must be calculated for the large temperature difference, and the operating temperature must be within the product's limits. These projects need a specialist engineer, not just a spray crew.

Thickness and thermal resistance: calculating R step by step

The thermal resistance of a homogeneous layer equals its thickness divided by its thermal conductivity. We use a conservative design conductivity k = 0.024 W/m·K, which lies within the range of aged and declared values in the datasheets reviewed. If your product datasheet gives a different value, substitute it into the same equation.

To sanity-check the calculation: the NCFI datasheet states R-6.7 per inch and R-13 at two inches (5.08 cm), close to our conservative figure for 5 cm (R-11.8). The difference comes from using a slightly higher k as a safety margin.

Foam and the Saudi Building Code SBC 601/602

The energy conservation code for residential buildings (SBC 602) and for non-residential buildings (SBC 601) sets maximum overall heat transfer coefficients (U) for envelope elements such as roofs and walls, and divides the Kingdom into three climate zones. We do not list zone U-values here so they are not quoted out of context; the binding numbers and calculation method are on the Saudi code standards page. In practice, foam counts as one of the roof layer resistances, and its thickness must be sufficient, together with the other layers, to achieve the required U-value.

A study published in ETASR (external source via the Consumer Safety Center) notes that about half of the electricity generated in Saudi Arabia is consumed by air conditioning of residential buildings, which drove the implementation of the code as part of Vision 2030 targets. Choosing thickness is therefore no longer only about comfort; for new buildings it is a matter of compliance.

Correct application procedure, step by step

Foam quality is made on site, so spraying conditions matter more than the product name. The following steps are based on manufacturer application guides and technical references; where they conflict, always follow the datasheet of the product used.

1. 1

   Initial survey

   Identify existing leaks, cracks and weak areas, measure falls and ponding locations, and list details (drains, pipes, AC bases, parapets).

2. 2

   Cleaning and preparation

   Remove dust, oils and loose layers by compressed air, vacuum, brooming or blasting; treat cracks; remove rust from metal sheet; and mask drains and openings.

3. 3

   Moisture and dew point check

   The surface must be dry with no visible moisture. Manufacturer guides prohibit spraying if a moisture meter reads above 10%, or if the surface temperature is within 5 °F (about 3 °C) of the dew point. This is critical in humid coastal cities in the morning.

4. 4

   Surface temperature and wind

   Application guides set a surface temperature range for spraying, such as 10–52 °C (50–125 °F) for one US system and +5 to +40 °C for a European system. One guide prohibits spraying in winds above 12 mph (about 19 km/h) without windscreens. Spraying on a very hot roof at summer noon may exceed product limits.

5. 5

   Primer where required

   Some substrates need a primer to improve adhesion, such as an acrylic primer on concrete, metal and wood in one system. Its type and application rate are set by the manufacturer.

6. 6

   Spraying in passes

   Foam is sprayed in passes, not in one go. Single-pass limits in the datasheets reviewed range from 13 to 38 mm (½–1½ inch) in one system and 15–45 mm in another, with a waiting interval between thick layers. Spraying thicker than the manufacturer's limit raises internal heat and causes defects.

7. 7

   Thickness and texture check

   Thickness is measured with a probe at distributed points, and texture is inspected: smooth to medium-coarse «orange peel» is acceptable, while «popcorn» or «tree bark» texture is rejected and resprayed. References require a total thickness of at least 2.5 cm (1 inch), and some manufacturers set it higher.

8. 8

   Topcoat

   Applied the same day, in at least two coats at least 12 hours apart, preferably with the first coat in a different color to reveal missed areas. Dry film thickness is then measured and the surface checked for pinholes and blisters.

For standard site procedures, including spray equipment and site safety requirements, see the field SOPs in the Azl academy.

Quality control: what is inspected, and when?

The owner is entitled to ask for these records in writing. The workmanship warranty is written, with its duration set according to the insulation type and roof condition; details are in the warranty policy.

Common defects, their causes and remedies

In complex cases, treatment starts with diagnosing the cause, not with immediate respraying, and if the old insulation has degraded over a large area, renewing the whole system may make more sense than patching.

Climate by region: what changes in application?

The foam itself does not change, but the spray window, the choice of topcoat and design priorities differ from one region to another:

• Riyadh and the Central region: high summer heat and dryness with a large day–night swing. The challenge is roof temperature at noon, so spraying during cooler hours and checking the product's upper temperature limit is preferred, with a reflective topcoat. Service details at foam insulation in Riyadh.
• Qassim: a continental climate similar to Riyadh with colder winters, and many agricultural warehouses and shinko hangars. See foam insulation in Buraidah.
• Dammam and the Eastern Province: high humidity near the coast and morning condensation on roofs. Here, measuring dew point and substrate moisture before every spray session is mandatory, and work may start late until the surface is dry. See foam insulation in Dammam.
• Tabuk and the North: cold winters in which the morning surface temperature may drop below the product minimum, so spray timing and a cold-weather product grade are selected accordingly. See foam insulation in Tabuk.

In all cases, the spray window is decided daily from site readings, not from seasonal averages.

How does foam reduce the electricity bill? The correct calculation

Conductive heat flow through a roof is calculated with a simple equation:

An illustrative example with explicit assumptions, not a measurement of a real building: a roof of 200 m², with an assumed existing layer resistance including air films of R = 0.35 m²·K/W, so U ≈ 2.86, and an average temperature difference ΔT = 20 K. After adding 5 cm of foam (R ≈ 2.08), total resistance becomes ≈ 2.43 and U ≈ 0.41.

Any electricity saving is therefore an estimate that depends on the building: the number of floors (the roof matters most for the top floor), AC efficiency, operating hours, and the condition of walls and windows. Use the tool below for an initial estimate with your own assumptions:

Price guide: how much does spray foam cost?

The indicative price of spray foam in the Saudi market is typically 30 to 55 SAR per square meter, excluding VAT; prices are indicative and are confirmed after inspection. Factors that determine where a project falls within this range:

• Required thickness and product density
• Topcoat type, number of coats and dry thickness
• Project area (small areas raise the price per square meter)
• Roof condition: removal of old insulation, crack repair, rust removal
• Number of details: drains, AC bases, pipes, parapets
• Access difficulty, height and safety requirements

For a complete roof insulation system (foam with additional layers and detailing), the indicative range rises to 45–85 SAR per square meter. Get a preliminary estimate for your project with the calculator below or on the cost calculator page:

Fire safety: foam is a combustible material

Although spray systems contain flame retardants, polyurethane foam remains a combustible organic material. One European system reviewed is classified Class E for reaction to fire under EN 13501-1, and US systems state a flame spread index below 75 in ASTM E84. These tests do not mean the material is «non-combustible».

In the International Building Code IBC, Chapter 26 (external source via the Consumer Safety Center), foam plastics are subject to limits on flame spread (75) and smoke development (450), and must generally be separated from the interior by an approved thermal barrier such as 0.5 inch (≈ 12.7 mm) gypsum wallboard, with specific exceptions for certain roof assemblies. One application guide states that steel decks may need a layer of Type X fire-rated gypsum board before foam is applied if local codes or the insurer require it.

Maintenance: how does the system last?

The IBHS guide recommends at least two inspections a year (before summer and after the rainy season in our context) to look for topcoat wear, exposed foam, blisters and mechanical damage. It states that topcoats need reapplication roughly every 10 to 20 years depending on their type, original thickness and other factors, and that well-maintained systems can exceed 30 years of service.

Avoid frequent walking on the roof without protective walkways, and do not fix new equipment with screws through the foam without re-detailing the fixing area. If you have a question about your specific roof, you can request an inspection to assess its condition before choosing the thickness and system.