As a retailer, it fills me with dismay, when customers come in, asking exactly the same questions that you are asking here. Within reason, most retailers, especially independents, will not only offer competitive prices for carpetsand the accessories, but they offer an expert fitting service, that quite simply, they have to supply legally. If something goes wrong, they have to legally sort it out to the expected standards.
What comeback do you have if you buy online, and later find out that the roll heights were different resulting in lines appearing in the carpet, or if there are issues with the consistancy within the foam (hard lumps are renowned in this underlay and can be felt 'in' the carpet)???
The retailer has a commitment to the customers to do things properly, supply quality product and put anything that goes wrong, right. They are also in business to make a living/profit, and they have had to commit to rent, taxes, wages, utilities etc etc etc. And yet, the general public feel they are being ripped off because a retailer is trying to make a profit.
When you buy underlays, gripper, doorbars etc online, do you know what you are buying? is the product suitable for the application? is there a better product available for different applications? what type of gripper should be used with different types of carpets? should you use short, medium or long pin gripper? standard gripper? concrete gripper? wood gripper? should the gripper be pinned, stick and pinned, drill and plugged or fully stuck? should the gripper be double banked? Will standard bars suffice, or would raised bars be more suited to the underlay choice? What underlays limit shading and trafficking? whats the difference in performance between rubber waffle and puFoam underlay? What advantage does rubber crumb hold over the previous underlays? Why do most shops not offer Felt underlays? whats the difference between Synthetic and natural Felt underlays? What underlay will enhance the performace of a particular type of carpeting? Why do some carpets HAVE to be laid on completely different underlays to those above? Why do some carpets have t be laid one day, but cust in the next?
Most professional and reputable carpet shops are not out to rip you off, they want to provide great advice and service, and shock horror, a small profit to support their families.
Carpet Right is renowned in the trade for a) Being expensive and b) damaging the image of the industry. Buying carpets is NOT a cheap purchase for anyone, at any end of the budget scale, and it's a decision that should be properly advised and specified to the budget that the customer has. If anyone thinks that 50% off plus an extra 20% off plus an extra 5% is an 'honest' pricing policy, have a long hard think about it. Carpet Right don't fit carpets by the way.
Now you can of course buy product on the internet, but unless you know the answer to all the above points - and more - then you take a risk of missing the opportunity to really tailor your carpet installation, in your property to the needs, requirements, and not necerssarily at the expense of 'paying more'.
To answer your question, the gap for the gripper will be dependent on the choice of underlay, carpet, type of subfloor, the fitters preferences and the type of gripper you are using, where in the room you are fitting, architrave shape, depth, stair type, stair shape, landing charactaristics and door bar type.if you manage to gripper the stairs correctly, as a DIY'er i'd be astonished.
And as a rule, most pro's would not recommend an 11mm puFoam on a staircase for a number of reasons, one of which is that there are better, more suitable types of underlay, upon which carpets will ewear betterm keep their appearence better and last longer and that are available at very little cost difference.
