How to Insulate a Floor from the Top – Guide

Insulation is one of the most rapid and cost-effective energy-saving solutions available for buildings. It’s not only about lowering greenhouse gas emissions, but it also offers an extra layer of protection for houses as well as a source of protection from damage.

How to insulate a floor from the top

How to Start Insulating a Floor from the Top

It’s essential to ensure that the floors are adequately insulated to minimize peak power loads in harsh weather situations.

The location of the insulation on a solid concrete floor is critical for either exposing or isolating the thermal mass of the concrete floor. The insulation allows the concrete floor to absorb any heat and keep it cool.

Suspended wooden flooring can also support insulation. Because of the low thermal mass of this configuration, it is more suited to intermittent heating applications.

For intermittent heating applications requiring a quick reaction time, having less thermal mass available to absorb heat from the system is advantageous; thus, putting the insulation layer beneath the screed but above the concrete slab or beam and block floor is ideal.

Required Material Type and Quantity

The installer must ensure that the batts on hand have a material R-value (Rm) that meets the scope of the work’s material R-value goal.

The number of batts needed is calculated by multiplying the project’s underfloor surface area in m2 by the manufacturer’s nominal coverage shown on the batt package.

Underfloor joists are usually allowed according to the manufacturer’s recommendations. This is an approximate estimate, and you should have some surplus stock on hand as well.

Required Tools and Equipment

Ascertain that the tools and equipment used to carry out the tasks are appropriate for the job. Prior to starting the job, check for tool problems, correct any flaws, and report your findings to your supervisor.

Recommended:

  • curved blade knife
  • serrated knife
  • ladder
  • hammer
  • mask
  • staple gun
  • knee pads
  • torch
  • tape measure
  • eyewear
  • shoes

Checking the Floors for the Correct Insulation Procedure

The thermal performance of buildings with relatively modest ground floor areas (mainly domestic properties) will be low if the ground floor is left uninsulated.

To improve thermal performance, the ground level should be completely insulated.

Complete ground floor insulation may not be essential for structures with substantial ground floor spaces (mainly non–domestic properties).

1-meter broadband of insulation around the perimeter might offer good thermal efficiency.

The distance between the top of the floor insulation surface or perimeter insulation upstand and the bottom of the wall insulation should be 150 / 220* mm minimum for a concrete floor and 200 mm minimum for a suspended wood floor to avoid cold bridging at the border of the floor.

Insulation Below a Floor Slab

The site should be prepped and foundations erected to damp proof course level, if necessary.

Over rolled hardcore, a thin sand blinding can be applied to produce a continuous flat surface free of protrusion.

Prior to installing the insulating boards, the damp proof membrane (minimum 250 micron / 1100 gauge polythene) should be put over well-compacted hardcore with seams properly lapped and folded to prevent groundwater penetration.

The membrane should be raised up the surrounding foundation walls until it reaches a height sufficient to link with or create the damp-proof membrane.

If two layers of insulation are necessary, they should be horizontally offset such that the board joints in the two adjacent layers do not coincide as much as feasible.

To avoid cold bridging, a strip of insulating board (minimum 20 mm thick) should be put vertically along the perimeter of the floor slab.

The top of the strip of insulation board should be level with the top of the floor screed, and the bottom should be level with and tightly butted up to the bottom of the horizontal floor insulation.

To prevent wet concrete from accessing the boards’ gaps and function as a vapor control layer, insulation boards should be covered with a polythene sheet (not less than 120 micron / 450 gauge).

Make sure the polythene sheet has 140 mm overlaps at the edges, is taped at the joints, and is turned up 90 mm at the walls.

How to insulate a floor from the top guide

The concrete slab and screed (or other flooring material) is then installed in a manner similar to that of an uninsulated floor. Prior to installing the floor finish, the concrete slab and screed should be allowed to dry.

Insulation Below a Floor Screed

Before installing the insulating boards, let the concrete slabs completely dry out (average 1 day per mm of slab thickness).

The slab’s surface should be smooth, flat, and devoid of projections. Floors made of beams and blocks should be leveled and grouted.

Prior to installing the insulating boards, the damp proof membrane (minimum 250 micron / 1100 gauge polythene) should be put over the concrete floor slab or beam and block floor, with seams firmly lapped and folded to prevent the entry of groundwater.

The membrane should be brought up the surrounding foundation walls until it is sufficiently above the height of the wall damp proof membrane.

The insulation boards should always be loose–laid and break–bonded, with joints lightly butted if two layers of insulation are required.

To avoid cold bridging, a strip of insulating board (minimum 15 mm thick) should be put vertically along the perimeter of the floor slab.

The top of the insulation board strip should be level with the top of the floor screed, and the bottom should be level with and tightly butted up to the bottom of the horizontal floor insulation.

To prevent the wet screed from reaching the seams between the boards and to function as a vapor control layer, insulation boards should be covered with a polythene sheet (not less than 120 micron / 450 gauges).

Make sure the polythene sheet has 140 mm overlaps at the edges, is taped at the joints, and is turned up 100 mm at the walls.

For home construction, use sand and cement screed with a minimum thickness of 60 mm and 70 mm elsewhere.

Insulation from Above the Floor Joists

Before starting the floor boarding process, the floorboard should be installed in suspended floor structures.

Cut the insulation boards to fit tightly between the floor joists. Because joist spacing might vary, measure the distance between them before cutting the boards.

Insulation boards should be supported on at least 20 mm x 20 mm treated softwood timber battens, patented galvanized steel saddle clips, or galvanized nails partially pushed into the side of the joists to ensure they are level with the top surface of the joists.

Battens/nails should be set at a height corresponding to the thickness of the board being installed, and nails should protrude 40 mm from the joist.

If two layers of insulation are necessary, they should be horizontally offset relative to each other as much as feasible so that the board joints in the two adjacent layers do not coincide.

Ensure that insulation boards are firmly installed between joists and that any gaps are filled with expanding urethane sealant.

Any small gaps between a joist and a perimeter wall should be insulated with a specially cut board that is supported on blocks attached to the bottom of the joists. Expanding urethane sealant should be used to cover gaps smaller than 20 mm wide.

Conclusion

Insulating a floor requires a lot of precision work and measurements. The floors must be coated, and the insulation must be appropriately fitted. We hope that this guide has been helpful in guiding you through the process.