Radiant heating changes the conditions a wood floor lives in. Warmth comes up through the boards instead of across the room, and the heating season dries the air and the wood more than an unheated floor would see. Oak can perform well over a heated subfloor, but the specification has to be written with the heating in mind from the first RFQ. This article covers why engineered construction is the usual starting point, which details belong in the specification, and which limits are set by someone other than the flooring factory.
Why a heated floor needs its own specification
Wood takes on and gives off moisture as the air around it changes. When it loses moisture it shrinks, and when it gains moisture it swells. Over a heated subfloor, the underside of each board sits closest to the heat source, and the heating cycle repeats every season. The result, if the floor is not specified and installed for it, can be seasonal gaps between boards, cupping or stress on the bond line.
None of this is unique to one supplier or one species. It is how wood behaves. The practical question is how to reduce the movement through construction, size and moisture control, and how to make sure the installation follows the rules of the heating system. For background on the systems themselves, the underfloor heating entry gives a general overview.
Who sets the limits
A heated floor involves several parties, and each one owns a different set of numbers. The flooring factory does not set surface temperatures or adhesive rules, and should not be asked to.
| Party | What they decide |
|---|---|
| Heating system maker | Maximum floor surface temperature, start-up and commissioning procedure, whether wood flooring is approved over the system, any limit on the thermal resistance of the floor covering |
| Adhesive maker | Whether the adhesive is approved for heated subfloors, subfloor preparation, open time and coverage |
| Installer | Subfloor readiness, acclimation on site, installation method, expansion allowances at walls and fixed objects |
| Designer or specifier | Construction, width, thickness and finish, within the limits above |
| Flooring factory | Building the board to the agreed specification, controlling moisture during production, and supplying the construction details the others need for their calculations |
The most useful thing a buyer can do early is collect the heating maker’s and adhesive maker’s requirements and send them with the RFQ. The factory can then confirm whether the requested build fits them before a sample is made.
Construction: why engineered is the usual choice
We produce three constructions: solid, 2-layer engineered and 3-layer engineered. Over radiant heating, engineered construction is the usual starting point because the core restrains the movement of the oak face.
- 3-layer engineered has an oak wear layer over a cross-layered core with a backing layer. It is designed for greater dimensional stability, and it is well suited to wider boards and larger open areas, which are common in heated floors.
- 2-layer engineered is a sawn oak wear layer bonded to a stable plywood core. It is a practical choice where overall floor height is limited, which matters when the heating system has already raised the build-up.
- Solid is one piece of oak through the full thickness. Solid boards are more demanding about the conditions they are laid over, and over a heated subfloor that demand increases. If solid is wanted, discuss it with the heating maker and installer before it goes into the specification.
On our line, adhesive spread, press pressure and press time are controlled for consistent bonding across the panel, and the bond between layers is checked. That matters more on a heated floor, where the bond line sees repeated temperature cycles. For a closer look at the two engineered builds, see 2-layer vs 3-layer engineered oak.
Thickness and wear layer
Thickness is a balance between two needs. A thinner board puts less wood between the heat source and the room, which is why heating makers often limit the thermal resistance of the floor covering. A thicker wear layer gives more allowance for sanding and refinishing over the life of the floor.
Our two standard builds are 5/8” (15mm) overall with a 3mm sawn wear layer and 3/4” (20mm) overall with a 6mm sawn wear layer. Other thicknesses from 3/8” (10mm) to 13/16” (21mm) are made to order. Ask the heating maker whether the overall thickness of your chosen build is within their guidance, and send the factory’s construction details (overall thickness, wear layer, core type) so that check can be made on real figures.
Width and length
Wider boards show more grain and give a calmer room, but each board carries more movement across its face. Narrower boards spread the same seasonal movement over more joints, so each gap stays smaller.
Widths already in production are 3-1/4” (83mm), 3-1/2” (89mm), 5” (127mm), 6” (152mm), 7-1/2” (190mm), 9” (229mm) and 9-1/4” (235mm). Other widths from 3” (76mm) to 12” (305mm) are made to order. If the design calls for a wide board over heating, pair it with the 3-layer construction and confirm the width with the heating maker and installer.
Length has less effect on movement than width. Random length runs from 12” to 86” (300 to 2200mm), and fixed length and long boards to 118” (3000mm) are cut to order.
Moisture: at the factory and on site
Moisture control happens in two places, and both matter.
At the factory. Timber is kiln-dried under controlled conditions and checked against the moisture target for the order before machining. Moisture is checked again before material moves down the line and before packing. If the installer or heating maker has a moisture requirement for flooring going over a heated subfloor, put it in the RFQ. The target is then confirmed in the quotation rather than assumed. Our article on wood moisture control in production explains the steps.
On site. The subfloor must be ready before any wood arrives. Heating makers normally set a commissioning procedure so a new slab is brought up to temperature and allowed to dry before flooring is laid. The installer checks the subfloor and the site conditions, and follows the acclimation guidance for the project’s location. These steps are outside the factory’s control, but they decide whether the floor performs.
Installation method
Our Tongue & Groove profile is machined on all four sides and is intended for glue-down or nail-down installation. Over a heated concrete slab, glue-down is common, and the adhesive must be one its maker approves for heated subfloors. The installer chooses the method based on the subfloor and the heating system, and that choice should be made before the order, since it can affect the construction and thickness. See how installation method shapes the specification.
Finish and edge detail
Grade, color, texture and sheen do not change how the floor behaves over heating, but they change how visible seasonal movement is. A fine joint line reads more strongly on a smooth, light floor with a square edge than on a brushed floor with a micro-bevel, where each board is already outlined. If some seasonal movement is expected, the edge detail is worth choosing with that in mind. See square edge vs micro-bevel.
What to put in the RFQ
- Construction: 3-layer or 2-layer engineered, and why
- Overall thickness and wear layer
- Width and length
- Heating type (water or electric) and the heating maker’s requirements for wood flooring
- Adhesive or installation method chosen by the installer
- Any moisture requirement for the flooring at dispatch
- Grade, color reference, texture, sheen and finish system
- Quantity in sq ft per SKU, and the delivery address or port
Working with Vu Uy Wood
Vu Uy Wood manufactures made-to-order solid and engineered French White Oak flooring in Song Than 3 Industrial Park, Ho Chi Minh City, and has done so since 2006. For heated floors, send the heating maker’s and adhesive maker’s requirements together with your specification, and we will confirm which construction and size fit them before the sample is made. The Specify page turns construction, width, grade and finish into a written brief you can send for quotation. We normally reply within one working day.