Need Under-Slab Vapor Retarder AND Under-Slab Void Forms?

There’s not a lot of information out there about this topic (what to do when you need both an under-slab vapor retarder AND an under-slab void), probably because this situation is a regional condition.  Not every part of the United States has the expansive soils that parts of Colorado have. 

The first part – the voids: 

Expansive soils on project sites often prompt geotechnical engineers to recommend under-slab voids, which are created by placing concrete for slabs on top of void forms, also known as carton forms.  Yes, we actually call for wet concrete to be placed on top of cardboard boxes… but not directly on top of the cardboard boxes!

The cardboard void forms, which are in contact with the soil, absorb moisture from the soil and degrade over time, while the concrete slab stays in place, so a void space is created between the bottom of the slab and the top of the earth.  This void allows expansive soils to expand, or swell, without impacting the slab.

The second part – the vapor retarder:

We specify under-slab vapor retarders to prevent water vapor from migrating through the floor slab-on-grade and damaging moisture-sensitive floor coverings or moisture-sensitive equipment.  (We do this everywhere, not just in Colorado.)  Without a vapor retarder between the slab and the soil, water in the soil can travel through the slab in vapor form, and then it can condense and form into liquid water once inside the building, where it can cause damage. 

Now – put the voids and the vapor retarder together:

The requirement for an under-slab void on a project calls for slightly different vapor retarder requirements than we normally specify.  My article on how to deal with this situation is published on the Construction Specifications Institute Denver Chapter website.  Click the link below for the article.

Words Matter… Especially in Contracts

I am not an attorney, but once in a while, I look at contracts all day long.  Why would I do that to myself?  Because these documents directly affect my work of preparing architectural construction specifications.

The contract documents for a construction project include contracting forms (such as the owner-contractor agreement), conditions of the contract (such as AIA A201), the drawings, and the specifications.  These documents, all together, make up the contract.

These documents should not conflict.  All too often though, because different parties prepare different documents, conflicts occur.

The owner-contractor agreement may say one thing, and the conditions of the contract may say the opposite.  The conditions of the contract may say one thing, and a Division 1 specification section may say the opposite.  A Division 1 specification section may say one thing, and a technical section of the specifications may say the opposite.  The technical sections of the specifications may say one thing, and the drawings say the opposite.  I’ve even seen General Conditions directly conflict with Supplementary Conditions!

My attorney and insurance professional friends will happily tell you that when a contract is ambiguous, courts usually side against the party who drafted the contract.  What does that mean for design professionals?

We have to coordinate, coordinate, coordinate.  If the Owner prepares General Conditions, the person preparing the specifications needs to make sure the specifications are coordinated with the Owner’s General Conditions.  If AIA A201 General Conditions are used, and the Owner just prepares Supplementary Conditions, the person preparing the specifications needs to make sure the specifications are coordinated with the Owner’s Supplementary Conditions.  If the Owner prepares General Conditions, Supplementary Conditions, and Division 1, the person preparing the technical specifications needs to make sure that his work product does not conflict with the Owner’s documents.  To protect his firm, the person signing the Owner-Architect Agreement should make sure that the Owner’s General and Supplementary Conditions do not conflict with provisions in the Owner-Architect Agreement.

And the issue on my mind all day today?  If the Owner has a Guide Specification/Technical Specification/Specification Standards sort of document that he expects design professionals to adhere to when preparing drawings and specifications, this guide SHOULD NOT CONFLICT with the Owner-prepared General Conditions and Supplementary Conditions.  Ah, yes, this should go without saying… However, I have spent days of my career as an architectural specifications consultant trying to coordinate conflicts among Owner-generated documents to make sure that the work I produce does not conflict with any other contract documents.

Again, I am not an attorney, but I have a feeling that uncoordinated Owner-prepared documents increase our risk as design professionals.  We have to produce coordinated documents, no matter what our Owner clients give us.  Every word matters!