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Insulating outside of block home?

I am building a earth-sheltered passive block home. I want to insulate it all from the outside. I have been trying to get Roxul Drainboard in 3.5 inches but cannot afford a whole truckload to do a small home. So I'm thinking of using 4 inches of XPS foam under slab and all walls.

Any suggestions for water proofing exterior of block and fastening XPS to all the walls?

Thank you.

Asked by michael holler
Posted Jul 11, 2014 8:34 AM ET
Edited Jul 11, 2014 1:09 PM ET


3 Answers

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For waterproofing, you will probably be using a dimple-mat system like Delta-MS or CertainTeed Platon.

Once you have chosen a manufacturer, you need to follow the manufacturer's installation instructions.

Below-grade exterior foam is usually held in place by the backfill material. Above-grade foam can be attached with large washers (roofing caps) and TapCon screws.

For more information, see How to Insulate a Basement Wall.

Answered by Martin Holladay, GBA Advisor
Posted Jul 11, 2014 1:15 PM ET


thank you for your advice on waterproffing below grade block wall . My question would be. Coat block with fiberous material then membrane,then foamboard? I know the importance of drying from interior to exterior so is this in right order? michael

Answered by michael holler
Posted Jul 14, 2014 10:28 AM ET


A concrete wall doesn't have to dry. It can be damp forever.

Concerning the order of the different layers, you should contact the company that manufactures the waterproofing system that you will be installing. Tell them that you want to include exterior rigid foam, and ask them how these products should be installed.

Answered by Martin Holladay, GBA Advisor
Posted Jul 14, 2014 10:50 AM ET

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