There may be many reasons you want to raise your fireplace. You can easily accomplish this customization. You need to think of the "Chimney Extension Kits" more as "Extension Kits" when looking to customize your outdoor fireplace kit. Chimney extensions are the most popular use, but not the only purpose. Each 12" extension is a half cube of Orion Block (14:14:18 blocks). This article and companion PDF will inform you on how you can turn those extensions into risers for your foundation. Note: This is for the Princeton and Fremont only. Rasing the Rockwell is not recommended. Click the image below for the PDF instructions that go with this article:
Before you begin, you will need to know how to excavate to allow for your concrete footing. Follow the instructions below for pouring a concrete pad (click for PDF). To raise your fireplace, I recommend pouring a concrete footing at ground level. Then you can build up from this footing. The blocks are 100mm thick(3-15/16"). Thus, you will want to use 4" increments to figure where the top of your concrete pad will be. This way, you will be able to build in courses of blocks.
I recommend allowing for an additional 3/8" to allow a mortar joint to set your block. This allowance is useful when you need to nail the final base elevation perfectly. A mortar joint will allow for fine-tuning and adjustment of your first course of blocks so that the stack ends up exactly where you need it. If there is no need for this exacting precision, you can always build off the finished concrete pad to get "close enough."
The footprint of your concrete pad may likely change. Usually, when raising a fireplace, it is to meet the elevation of an existing patio. More often than not, the patio will have a straight side. Therefore, we will make some small adjustments to achieve this. One preferred method is to have only the weight of the hearth on the existing patio. The mass of the fireplace and wood boxes will be on your raised structure. Only Classic boxes can achieve this. You will want to slide them 4" forward, so the foot of the boxes are flush with the front of your firebox:
Other times, you may need to raise your entire fireplace and wood boxes with no additional modifications. You can easily achieve this customization by using the same chimney extension kits. It takes a unique layout depending on which wood boxes you are pairing with your fireplace. Below you will see the layouts that are included in the foundation riser PDF:
As you can notice, my Orion building system is highly customizable and extendable. Hopefully these plans will help you with your build. As always, direct any questions to email@example.com