documents: originals vs. copies

I know the Consulate requests original documents instead of copies and this is understandable in the case of birth certificates and passports.

I am wondering about what is accepted for other documents, specifically accomadation.  We are going to stay with my beau's relative while we get settled and want to send proof of this.  This relative is a bit unsure of handing over the dead to his house to us because it is very costly and expensive to replace.  Is it alright to have a regular photocopy of this deed accompanied by a letter written that he will allow us to stay there temporarily?
MUST we get certified copies of this, or with these sorts of documents is it alright to have just a regular photocopy?  If we must have a certified copy, where can this be done, how much does it cost, and how much notice is needed?

Deary me, small thing, but I get a bit worried.
Thanks in advance for advice.
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I'd have him get a certified copy which can be done at any solicitor's office and the charge should be pretty minimal (maybe £5-£7 at best...depends on the solicitor).  Having the letter will also help.  If he just sends in a regular photo copy, you run the risk of it being rejected. I would err on the side of caution.

When we were getting our fiancee visa we needed the deed to my in-laws house as well. As I hadn't brought this with me (but I did bring a signed letter from them giving us permission), I had to call them and they took their original deed and faxed it to the Chicago consulate. The chicago people were perfectly happy with that, but I'm not sure if that's a steadfast rule, or up to the individual clerk's discretion. Just to make yourself feel better, you should drop the consulate (whichever one you're using) an email or a quick phonecall... put your mind at ease.